Virus-virus interactions impact the population dynamics of influenza and the common cold

Year-round infectome profiling of acute febrile respiratory illness unveiled complex epidemiological dynamics postlifting of COVID-19 restrictions

OBJECTIVES

Following the lifting of COVID-19 nonpharmaceutical interventions in China, respiratory infections surged, though the specific causes remained unclear. This study provided a comprehensive overview of the infectome in patients with acute febrile respiratory illness (AFRI) to inform disease surveillance.

METHODS

Between March 2023 and February 2024, 1163 oropharyngeal swabs from AFRI patients and 338 from healthy individuals were collected in Shenzhen. Meta-transcriptomic sequencing was employed for microbial analysis.

RESULTS

We identified 14 viruses and 10 bacteria species known to cause human disease. Influenza virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Streptococcus pneumoniae, and redondovirus were the most common, with a negative correlation between H3N2 and SARS-CoV-2. Notably, we detected certain enterovirus subtypes (e.g., Coxsackievirus A6 and Echovirus 30), previously overlooked pathogens (e.g., redondovirus), and rare pathogens like Streptococcus pseudopneumoniae. Comparisons revealed five pathogens showed significantly higher abundance in patients than in controls, despite no significant differences for others probably due to their limited number of positive pools. Seasonal shifts in microbial diversity and composition were observed, with climate factors like temperature and precipitation playing a role. Phylogenetic analysis revealed changes in genotype diversity and dominant pathogen lineages.

CONCLUSION

This study highlighted complex pathogen infections in AFRI patients following COVID-19 restrictions, demonstrating the value of meta-transcriptomics over PCR-based methods for more detailed pathogen surveillance.

Epidemiological and clinical profile of viral respiratory infections in children under 5 years at pre- and post-COVID-19 era in Praia, Cabo Verde

BACKGROUND

The coronavirus disease-19 (COVID-19) pandemic has affected global health, influencing the prevalence of different respiratory pathogens. The aim of this study is to evaluate the distribution of agents causing acute respiratory infections in children under 5 years old before and after the COVID-19 pandemic in Praia, Cabo Verde, and to describe associated clinical variables.

METHODS

Conducted at the University Hospital Dr. Agostinho Neto, this study replicated methods from a previous work from 2019 (Correia et al. 2021). Nasopharyngeal samples were analysed using FilmArray® Respiratory Panel 2.1 (BioFire) to identify agents of acute respiratory infections. Molecular identification of human respiratory syncytial virus subtypes was performed using a real-time duplex reverse transcription polymerase chain reaction. Statistical analysis was performed using IBM SPSS version 29 and R 3.5.1 software.

RESULTS

In 2022, 86.5% (83/96) of nasopharyngeal samples were positive for at least one pathogen. Human rhinovirus/human enterovirus was the most frequent agent, followed by human respiratory syncytial virus, adenovirus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Co-infections were observed in 43.3% of positive cases. Infection rates were significantly higher in children under 1 year of age, particularly for SARS-CoV-2 and human respiratory syncytial virus. Seasonal variations were observed, with human respiratory syncytial virus predominating in November, SARS-CoV-2 in January and human parainfluenza virus-4 in May. Molecular analysis of human respiratory syncytial virus revealed a shift in subtype prevalence, with both human respiratory syncytial virus-A and -B co-circulating in the pre-pandemic period, whereas only human respiratory syncytial virus-B was detected in the post-pandemic period.

CONCLUSION

Our data indicate changes in the distribution of respiratory viruses in the post-pandemic period compared to pre-pandemic period. The high prevalence of co-infections highlights the complexity of acute respiratory infection aetiology, emphasising the need for enhanced respiratory virus surveillance systems in Cabo Verde. Identifying seasonal trends and risk factors can contribute to targeted interventions and improved public health strategies to mitigate the burden of acute respiratory infections in young children.

The rules in co-infection of multiple viruses across diverse lineages in a fungal host

Viruses, ubiquitous non-cellular organisms, pose significant threats to human health and to the agricultural productivity of both livestock and crops. Emerging evidence indicates that multiple viruses can infect a single host, and viral co-infection can exert a profound influence on host physiology. However, our understanding of the prevalence of co-infection and the compatibility of phylogenetically distant viruses is still limited. In this study, we surveyed 406 field strains of the plant fungal pathogen Botrytis cinerea and identified 76 mycoviruses. Strikingly, 404 strains were co-infected with two or more viruses, with some harboring up to 25 viruses simultaneously. We discerned significant preference patterns among viruses in their host. Specifically, we identified "one-to-one" and "two-to-one" rules, wherein one or two viruses could be used to reliably predict the presence or absence of other viruses in the same host, and validated these predicted rules by using five B. cinerea strains. Furthermore, through the RNA-sequencing approach, we uncovered B. cinerea genes associated with the differences caused by different sets of co-infecting viruses. These are implicated in integral components of membrane, transmembrane transporter activity, autophagy pathways, mitophagy pathway, fatty acid biosynthetic process, sphingolipid metabolism, and glycosphingolipid biosynthesis. Our findings underscore the high prevalence of co-infection by multiple viruses in a fungal host within a population and highlight compatibility dynamics among phylogenetically diverse viruses. These insights contribute to our understanding of viral ecology and hold promise for informing strategies to manage viral diseases effectively.

IMPORTANCE

Viruses, pervasive threats to both humans and agriculture, often infect hosts concurrently, profoundly impacting physiology. Despite this, the prevalence and compatibility of co-infecting viruses remain poorly understood. In the study of 406 Botrytis cinerea strains, we discovered a striking phenomenon: 404 out of the 406 strains hosted multiple viruses, some with up to 25 at once. Through rigorous analysis, we unveiled distinct preference patterns among these viruses within hosts, identifying predictive co-infection rules validated by experimentation. Furthermore, we identified genes linked to these dynamics, shedding light on critical cellular processes involved in the regulation of the co-infection rules. These findings highlight the widespread nature of viral co-infection and offer insights crucial for effectively managing viral diseases.

Influenza A virus interferes with respiratory syncytial virus in mice and reconstituted human airway epithelium

Epidemiological studies suggest that respiratory syncytial virus (RSV) and influenza A virus (IAV) might interfere with each other. Viral interference mainly relies on interferon production elicited by a first virus that reduces the replication of a second virus. In this paper, we first investigated the interactions between RSV-A2 and influenza A(H1N1)pdm09 in BALB/c mice infected with each single virus or both viruses simultaneously or sequentially before, at the peak of interferon elicited by each virus, or after that peak. IAV reduced by almost 3.0 logs the replication of RSV administered at the peak of interferon induced by influenza, but the opposite was not true. However, IAV-infected mice challenged with RSV or the vehicle lost more weight and had a lower survival rate compared to single infections. Interferon expression, cytokine levels, and pulmonary inflammation were almost similar between groups. Disease worsening was attributed to an aggravation of IAV-induced pulmonary congestion following intranasal instillation of fluid (with or without RSV). In human airway epithelia, IAV also interfered with RSV replication. Viral interference was dependent on the timing and sequence of infections but not on differential interferon susceptibilities. Overall, our results help to understand the mechanisms of the interaction between two major respiratory viruses.IMPORTANCERespiratory syncytial and influenza viruses may interfere with each other based on epidemiological studies. It is suggested that a first virus may induce the production of interferon and interfere with the replication of a second unrelated virus. Our data showed that the influenza A virus interferes with respiratory syncytial virus replication in mouse lungs, but the opposite was not observed. In reconstituted human airway epithelia, viral interference was dependent on the timing and sequence of infections but not on differential interferon susceptibilities. Understanding the mechanisms of interaction between respiratory viruses may help the development of prophylactic or therapeutic modalities.

Population-level respiratory virus-virus interactions, Puerto Rico, 2013-2023

BACKGROUND

Understanding virus-virus interactions is important for evaluating disease transmission and severity. Positive interactions suggest concurrent circulation, while negative interactions indicate reduced transmission of one virus when another is prevalent. This study examines interactions among seven respiratory viruses using a Bayesian approach that accounts for seasonality and long-term trends.

METHODS

We analyzed data from 43,385 acute febrile illness cases in the Sentinel Enhanced Dengue Surveillance System in Puerto Rico (2013-2023). Viruses studied included influenza A (IAV), influenza B (IBV), respiratory syncytial virus (RSV), human parainfluenza viruses 1 and 3 (HPIV-1, HPIV-3), human adenovirus (HAdV), and human metapneumovirus (HMPV). Wavelet coherence analysis investigated synchronous or asynchronous viral co-variation, while a Bayesian hierarchical model estimated pairwise interactions.

RESULTS

Among 43,385 participants, 26.0% tested positive for at least one virus, with IAV (9.5%), HAdV (4.1%), RSV (3.6%), and IBV (3.6%) being most frequent. Coinfections occurred in 0.5% of cases, often involving HAdV. Wavelet coherence identified significant synchronization among RSV/HMPV, HPIV-1/HMPV, and other virus pairs, with minimal coherence during the COVID-19 pandemic. Bayesian modeling suggested five virus-virus associations: four positive (RSV/HPIV-3, HMPV/HPIV-1, IBV/HAdV, IBV/HMPV) and one negative (IAV/HAdV). However, when restricting the analysis to the prepandemic period, fewer associations remained statistically credible.

CONCLUSION

Respiratory viruses in Puerto Rico demonstrate patterns of co-circulation that may reflect complex interactions, but these associations appear context-dependent. Findings highlight the need for continued surveillance to better understand virus-virus dynamics and their implications for public health interventions.

Unseasonal respiratory syncytial virus epidemics during the COVID-19 pandemic: Relationship between climatic factors and epidemic strain switching

OBJECTIVES

The COVID-19 pandemic has altered respiratory syncytial virus (RSV) epidemic patterns. However, the influence of climatic and virological factors on RSV outbreaks remains unclear. We examined RSV incidence in Okinawa, Japan; Taiwan, China; and Florida, USA before and after the COVID-19 pandemic, focusing on the effects of population mobility and climate.

METHODS

We analysed correlations among RSV incidence, human mobility, and climate before and after the pandemic. Additionally, we conducted a phylogenetic analysis of the second variable region of RSV G proteins using viral genomes isolated from patients with acute respiratory tract infections in Okinawa.

RESULTS

Annual RSV epidemics in Okinawa were not correlated with post-pandemic human mobility. The temperature and humidity ranges at the onset of RSV epidemics differed between the pre- and post-pandemic periods, with decreased standard deviations. Genetic analysis of RSV strains from 2020 to 2022 revealed a cluster with low genetic diversity, which differed markedly from pre-2019 and 2023 prevalent strains.

CONCLUSION

Reduced human migration led to an RSV epidemic caused by an indigenous endemic strain, highlighting the natural relationship between epidemics and climatic factors. These findings could aid in developing effective prediction and control programs for RSV epidemics and optimising vaccine programs.

SARS-CoV-2 infection in the Indigenous Pataxó community of Southern Bahia, Brazil: second wave of transmission and vaccine effects

Indigenous people are at risk of several infectious diseases, including viruses that affect the respiratory system. In a previous study, we demonstrated how the Pataxó ethnic group, in the southernmost region of Bahia State, Brazil, was disproportionately affected during the first wave of COVID-19. Here, we provide an overview of how this community was affected by the second wave of the disease, evaluating the impact of vaccination on SARS-CoV-2 transmission. Prospective study data was grouped by Epidemiological Weeks 3/2021-43/2022, during which vaccine effects were analyzed and new variants of concern (VOC) emerged. The second wave produced a decreasing trimodal moving average curve, with an incidence rate of 4,407.2/100,000 inhabitants. Mobility and precarious work situations linked to tourism and craft trade increased infection rates in some villages. Risk factors for infection and severity (female sex, older age, and comorbidities) were determinants, but mortality was lower. Individuals with two doses of vaccine (Vac) developed more symptoms than the unvaccinated, but were less likely to have dyspnea. The mean time for COVID-19 symptoms to develop was longer in those with Vac (x̅ = 27 weeks) compared to those who received only one dose (x̅ = 12 weeks, p ≤ 0.001). Vac individuals who received booster shots, VacB1 and VacB2, had infection rates of 7.4% and 0%, respectively. The detrimental impact of COVID-19 once again highlights the persistence of health and socioeconomic inequities in this ethnic group. Moreover, the vaccines failed to prevent transmission, possibly due to mutated VOCs, but they may have protected this group against severe symptoms and extended the transmission period.

Making sense of the virome in light of evolution and ecology

Understanding the patterns and drivers of viral prevalence and abundance is of key importance for understanding pathogen emergence. Over the last decade, metagenomic sequencing has exponentially expanded our knowledge of the diversity and evolution of viruses associated with all domains of life. However, as most of these 'virome' studies are primarily descriptive, our understanding of the predictors of virus prevalence, abundance and diversity, and their variation in space and time, remains limited. For example, we do not yet understand the relative importance of ecological predictors (e.g. seasonality and habitat) versus evolutionary predictors (e.g. host and virus phylogenies) in driving virus prevalence and diversity. Few studies are set up to reveal the factors that predict the virome composition of individual hosts, populations or species. In addition, most studies of virus ecology represent a snapshot of single species viromes at a single point in time and space. Fortunately, recent studies have begun to use metagenomic data to directly test hypotheses about the evolutionary and ecological factors which drive virus prevalence, sharing and diversity. By synthesizing evidence across studies, we present some over-arching ecological and evolutionary patterns in virome composition, and illustrate the need for additional work to quantify the drivers of virus prevalence and diversity.

The Role of Viral Interference in Shaping RSV Epidemics Following the 2009 H1N1 Influenza Pandemic

BACKGROUND

Disruptions in respiratory syncytial virus (RSV) activity were observed in different countries following the 2009 influenza pandemic. Given the limited use of non-pharmaceutical interventions, these disruptions provide an opportunity to probe viral interference due to the out-of-season epidemics. The objectives of the study are twofold: to characterize atypical RSV activity in the United States (US) and to explore the mechanisms underlying changes in RSV epidemics following the pandemic.

METHODS

Laboratory-confirmed RSV cases across 10 US regions from June 2007 to July 2019 were analyzed. A dynamic time warping method was used to characterize RSV activity in different seasons. A two-pathogen model was constructed to explore viral interference mechanisms. A sampling-importance-resampling method was applied to estimate the effects of viral interference.

RESULTS

We found that RSV activity was reduced following the influenza pandemic in the 2009/10 season across all regions in the US. By contrast, we found an enhanced but delayed RSV epidemic across the US in the 2010/11 season. Using a mathematical model, we explored three potential viral interference mechanisms that could explain the change of RSV activity following the pandemic. The pandemic influenza may interfere with RSV to reduce susceptibility to RSV coinfection, or shorten the RSV infectious period, or decrease RSV infectivity in co-infections.

CONCLUSIONS

This study provides statistical evidence for atypical RSV seasons following the influenza pandemic in the US and sheds light on viral interference mechanisms affecting RSV epidemics, offering a model-fitting framework for analyzing surveillance data at the population level.

Hidden in plain sight: the impact of human rhinovirus infection in adults

BACKGROUND

Human rhinovirus (HRV), a non-enveloped RNA virus, was first identified more than 70 years ago. It is highly infectious and easily transmitted through aerosols and direct contact. The advent of multiplex PCR has enhanced the detection of a diverse range of respiratory viruses, and HRV consistently ranks among the most prevalent respiratory pathogens globally. Circulation occurs throughout the year, with peak incidence in autumn and spring in temperate climates. Remarkably, during the SARS-CoV-2 pandemic, HRV transmission persisted, demonstrating its resistance to stringent public health measures aimed at curbing viral transmission.

MAIN BODY

HRV is characterised by its extensive genetic diversity, comprising three species and more than 170 genotypes. This diversity and substantial number of concurrently circulating strains allows HRVs to frequently escape the adaptive immune system and poses formidable challenges for the development of effective vaccines and antiviral therapies. There is currently a lack of specific treatments. Historically, HRV has been associated with self-limiting upper respiratory infection. However, there is now extensive evidence highlighting its significant role in severe lower respiratory disease in adults, including exacerbations of chronic airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD), as well as pneumonia. These severe manifestations can occur even in immunocompetent individuals, broadening the clinical impact of this ubiquitous virus. Consequently, the burden of rhinovirus infections extends across various healthcare settings, from primary care to general hospital wards and intensive care units. The impact of HRV in adults, in terms of morbidity and healthcare utilisation, rivals that of the other major respiratory viruses, including influenza and respiratory syncytial virus. Recognition of this substantial burden underscores the critical need for novel treatment strategies and effective management protocols to mitigate the impact of HRV infections on public health.

CONCLUSION

This review examines the epidemiology, clinical manifestations, and risk factors associated with severe HRV infection in adults. By drawing on contemporary literature, we aim to provide a comprehensive overview of the virus's significant health implications. Understanding the scope of this impact is essential for developing new, targeted interventions and improving patient outcomes in the face of this persistent and adaptable pathogen.

Trends of respiratory viruses and factors associated with severe acute respiratory infection in patients presenting at a university hospital: a 6-year retrospective study across the COVID-19 pandemic

Background

The COVID-19 pandemic significantly disrupted the epidemiology of respiratory viruses, altering seasonal patterns and reducing circulation. While recovery trends have been observed, factors associated with severe acute respiratory infections (SARIs) during pre- and post-pandemic periods remain underexplored in middle-income countries.

Objective

This study aimed to analyze the trends in respiratory virus circulation and identify factors associated with SARI in patients attending a tertiary care university hospital in western Mexico over a six-year period spanning the pre-pandemic, pandemic, and post-pandemic phases.

Methods

A retrospective study was conducted using data from 19,088 symptomatic patients tested for respiratory viruses between 2018 and 2024. Viral trends were analyzed through interrupted time series (ITS) modeling, incorporating locally estimated scatterplot smoothing (LOESS) and raw positivity rates. Additionally, ITS analysis was performed to evaluate temporal changes in SARI proportions across different phases of the pandemic. Multivariate logistic regression models were applied to determine independent risk factors for SARI across different time periods.

Results

During the pandemic (2020-2021), respiratory virus positivity rates significantly declined, particularly for influenza, which experienced a sharp reduction but rebounded post-2022. Respiratory syncytial virus (RSV) demonstrated a delayed resurgence, whereas other respiratory viruses exhibited heterogeneous rebound patterns. ITS modeling of SARI proportions revealed a significant pre-pandemic increasing trend, followed by a slower rise during the pandemic, and a sharp post-pandemic drop in early 2022, before resuming an upward trajectory. Among older adults (>65 years), a marked increase in SARI was observed at the beginning of the pandemic, while younger groups showed more stable patterns. Logistic regression identified advanced age, male sex, cardiovascular disease, obesity, and immunosuppression as major risk factors for SARI, while vaccination consistently showed a protective effect across all periods and subgroups.

Conclusion

The COVID-19 pandemic induced persistent shifts in respiratory virus circulation, disrupting seasonal dynamics and modifying the burden of SARI. The findings underscore the importance of continuous surveillance, targeted vaccination programs, and early diagnostics to mitigate severe outcomes. These results highlight the need for adaptive public health strategies in middle-income countries to address evolving respiratory disease threats.

The added value of diagnostics to characterize age-specific patterns of respiratory viral infections and coinfections and to detect emerging threats

BACKGROUND

Pandemic restrictions caused variation in respiratory virus circulation until the winter of 2022/23. The aim of this study was to monitor respiratory virus cases in the 2023/24 epidemic season.

METHODS

Children and adults attending Sapienza University Hospital for acute respiratory infections (October 2023-June 2024) were tested for respiratory viruses via molecular methods.

RESULTS

Of the 1121 patients included, 880 (78%) were positive for rhinovirus (HRV, 32%), Influenza A (IAV, 29%), and respiratory syncytial virus (RSV, 28%). RSV is more common in infants, and IAV is more common in adults, whereas HRV is more common in children aged 1-5 years. IAV, RSV and HRV cocirculate in winter; HRV cases also occur in spring, along with Influenza B (IBV) and other viruses. Despite circulating in the same weeks, the number of observed coinfections was much lower than that predicted for IAV and RSV (p <.0001) and lower also for the IAV/IBV, IBV/RSV and RSV/HRV pairs (p <.0001, p =.0059, p =.015, respectively). IAV and RSV cocirculated with different patterns in different age groups. In fact, in children aged 1-5 years, the RSV peak preceded that of IAV, whereas in older age groups, the RSV peak occurred toward the end of IAV circulation. Sequencing of HRV/EV cases in spring revealed 25 HRV genotypes and two EV-C105 cases.

CONCLUSIONS

Respiratory viruses can cause age-specific seasonal peaks that are modulated by viral interference phenomena. Molecular diagnostic data should be integrated with surveillance programs to characterize seasonal circulation patterns of common respiratory viruses and to rapidly detect the next pandemic threat.

Periodontal Status and Herpesiviridae, Bacteria, and Fungi in Gingivitis and Periodontitis of Systemically Compromised Pediatric Subjects: A Systematic Review

BACKGROUND

Gingivitis and periodontitis are microbially associated diseases, with some features characteristic of pediatric age and others linked to systemic diseases. While the role of periodontal pathogenic bacteria is well recognized, the contribution of fungi and viruses, particularly Herpesviridae, remains controversial. Studies in adults have highlighted the presence of Herpesviridae, but evidence in pediatric subjects, especially systemically compromised, is limited. This systematic review aimed to assess periodontal status (e.g., health, gingivitis, periodontitis, necrotizing gingivitis, and/or periodontitis) and the subgingival and/or salivary microbial (bacterial, viral, and fungal) profile in systemically compromised pediatric (≤18 years) subjects with gingivitis and/or periodontitis compared to clinical periodontal health.

METHODS

The review protocol was registered on PROSPERO (CRD42024597695) and followed the PRISMA statement. Data from eight studies were descriptively analyzed and qualitatively assessed through ROBINS-I and JBI tools.

RESULTS

CMV was frequently detected, particularly in necrotizing gingivitis (19.40%). EBV was found in necrotizing gingivitis (20.69%) and periodontitis (10.34%); HSV was mainly associated with gingivitis and necrotizing gingivitis. Bacteria species in periodontitis included Porphyromonas gingivalis, Tannerella forsythia, Fusobacterium, and Campylobacter species. Candida albicans was detected in periodontitis, suggesting a fungal involvement in the disease's pathogenesis. Although the bacterial and fungal profile was not investigated, limited viral presence was noted in subjects with healthy periodontium, indicating a stable microbiome.

CONCLUSIONS

These findings underscore the dynamics of microbial interactions in the progression of periodontal disease in systemically compromised pediatric subjects.

Respiratory Symptoms and Health Outcomes of Rhinovirus and Influenza Virus Infections: Implications of Asthma, Diabetes Mellitus and Allergic Rhinitis in Rhinovirus C Infection

Rhinovirus (RV), classified into RV-A, RV-B, and RV-C, is a prevalent cause of respiratory tract infections (RTIs). Here, we analysed RV infection and its clinical implications among outpatients with acute upper RTIs. Demographic data, baseline comorbidities, clinical symptoms, and health outcomes of RV-infected patients (n = 849) were compared with influenza (n = 417). Multivariable logistic regression was employed to evaluate predictors and health outcomes over a 1-year follow-up period. RV infections predominantly presented with cough, nasal discharge, and sore throat, whereas fever was more prevalent in influenza cases. RV-C-infected individuals with diabetes mellitus (adjusted odds ratio [aOR] 3.6; 95% CI 1.7-7.2; p = 0.001) and asthma (aOR 1.9; 95% CI 1.0-3.5; p = 0.047) showed a higher likelihood of experiencing severe acute respiratory symptoms. RV-C patients with comorbidities were twice more likely to have primary care visits due to RTIs within 1 year (aOR 2.4; 95% CI 1.4-4.4; p = 0.003). Asthma (aOR 3.8; 95% CI 1.9-7.2; p < 0.0001) and allergic rhinitis (aOR 2.9; 95% CI 1.0-8.0; p = 0.042) were key predictors of increased RTI-related primary care visits. RV infection, particularly in individuals with asthma, allergic rhinitis and diabetes, poses a significant disease burden similar to that of influenza.

Human Metapneumovirus: an emerging respiratory pathogen and the urgent need for improved Diagnostics, surveillance, and vaccine development

Human Metapneumovirus (HMPV) is a re-emerging respiratory pathogen causing significant morbidity and mortality, particularly among young children, the elderly, and immunocompromised individuals. First identified in 2001, HMPV has since been recognised as a leading cause of acute respiratory tract infections (ARTIs) worldwide. Its transmission occurs through droplets, direct contact, and surface contamination, with crowded spaces and healthcare facilities serving as key environmental amplifiers. HMPV's clinical manifestations, ranging from mild cold-like symptoms to severe pneumonia, often overlap with those of other respiratory pathogens like RSV and COVID-19, complicating timely diagnosis and management. Despite advancements in molecular diagnostics, the limited accessibility of these tools in low-resource settings presents a challenge. Preventive measures, such as hygiene practices and physical distancing, remain critical, as no approved vaccines or targeted antiviral therapies are currently available. However, promising innovations, including AI-guided vaccine design and portable diagnostic tools, highlight the potential for future breakthroughs. This article highlights the urgent need for enhanced surveillance, scalable diagnostics, and intensified research into vaccines and therapeutic strategies. By addressing these gaps, HMPV's global burden can be significantly mitigated, improving outcomes for high-risk populations, and strengthening preparedness against respiratory virus outbreaks.

The role of the gut microbiota in regulating responses to vaccination: current knowledge and future directions

Antigen-specific B and T cell responses play a critical role in vaccine-mediated protection against infectious diseases, but these responses are highly variable between individuals and vaccine immunogenicity is frequently sub-optimal in infants, the elderly and in people living in low- and middle-income countries. Although many factors such as nutrition, age, sex, genetics, environmental exposures, and infections may all contribute to variable vaccine immunogenicity, mounting evidence indicates that the gut microbiota is an important and targetable factor shaping optimal immune responses to vaccination. In this review, we discuss evidence from human, preclinical and experimental studies supporting a role for a healthy gut microbiota in mediating optimal vaccine immunogenicity, including the immunogenicity of COVID-19 vaccines. Furthermore, we provide an overview of the potential mechanisms through which this could occur and discuss strategies that could be used to target the microbiota to boost vaccine immunogenicity where it is currently sub-optimal.

Prevalence and distribution of respiratory pathogens in pediatric acute respiratory infections in Putian, China

BACKGROUND

Acute Respiratory Infections (ARIs) are a significant source of morbidity among pediatric populations. This study aimed to investigate the prevalence and distribution of respiratory pathogens in pediatric ARIs in Putian, China.

METHODS

This retrospective study included 3,790 pediatric patients with suspected ARIs, evaluated between March 2023 and February 2024. Nasopharyngeal swabs were obtained and analyzed via reverse-transcription polymerase chain reaction (RT-PCR) to detect eleven common respiratory pathogens. Statistical analyses were conducted to evaluate the distribution of these pathogens across various patient demographics, including gender, age, and season.

RESULTS

This study included 3,790 pediatric patients under 14 years (median age: 4.3 years, IQR: 1-7). Pathogen positivity was 78.9%, with higher rates in school-age children and during autumn and winter (P < 0.001), with Mycoplasma pneumoniae (Mp) as the most common pathogen (33.4%), followed by human rhinovirus (HRV; 15.0%) and human respiratory syncytial virus (HRSV; 12.1%). Single-pathogen detections dominated (81.9%), while co-detections (18.1%) were primarily dual-pathogen cases, with HRV + Mp as the leading combination. Pathogen distribution varied significantly by age: Mp detection rates escalated with age, peaking in school-age children, while HRSV and HRV predominated in infants and toddlers. Seasonal trends revealed distinct pathogen activity: Influenza A (InfA) peaked during spring, Mp during autumn and winter, and HRSV during summer (P < 0.001). Logistic regression analysis identified significant associations: InfA, human adenovirus (HADV), and Influenza B (InfB) were linked with acute upper respiratory infections (AURIs), while Mp, human metapneumovirus (HMPV), human parainfluenza virus (HPIV), and HRSV correlated with acute lower respiratory infections (ALRIs) (P < 0.05).

CONCLUSION

This study provides comprehensive insights into the prevalence and temporal patterns of respiratory pathogens among hospitalized children with ARIs in Putian, China. Mp, HRV, and HRSV were the predominant pathogens, with significant variations by age and season. Limitations include the one-year duration and the focus on hospitalized patients. Future studies should extend surveillance to outpatient and emergency settings to obtain a broader understanding of ARI epidemiology.

The role of viral interference in shaping RSV epidemics following the 2009 H1N1 influenza pandemic

Background

Disruptions in respiratory syncytial virus (RSV) activity were observed in different countries following the 2009 influenza pandemic. Given the limited use of non-pharmaceutical interventions, these disruptions do provide an opportunity to probe viral interference due to the out-of-season epidemics. The objectives of the study are twofold: to characterize atypical RSV activity in the United States (US) and to explore the mechanisms underlying changes in RSV epidemics following the pandemic.

Methods

Laboratory-confirmed RSV cases across 10 US regions from June 2007 to July 2019 were analyzed. A dynamic time warping method was used to characterize RSV activity in different seasons. A two-pathogen model was constructed to explore viral interference mechanisms. A sampling-importance resampling method was applied to estimate the effects of viral interference.

Results

We found that RSV activity was reduced following the influenza pandemic in the 2009/10 season across all regions in the US. By contrast, we found an enhanced but delayed RSV epidemic across the US in the 2010/11 season. Using a mathematical model, we identified three potential viral interference mechanisms that could explain the change of RSV activity following the pandemic. The pandemic influenza may interfere with RSV to reduce susceptibility to RSV coinfection, or shorten the RSV infectious period, or decrease RSV infectivity in co-infections.

Conclusions

This study provides statistical evidence for atypical RSV seasons following the influenza pandemic in the US and sheds light on viral interference mechanisms affecting RSV epidemics, offering a model-fitting framework for analyzing surveillance data at the population level.

Respiratory pathogens detected in specimens collected for COVID-19 surveillance in Zambia

Background

In Zambia, knowledge on the landscape of respiratory pathogens that circulated during the coronavirus disease 2019 (COVID-19) pandemic is limited.

Aim

This study investigated respiratory pathogens that circulated in Zambia during the COVID-19 pandemic.

Setting

Nasopharyngeal specimens collected between July 2020 and July 2021 for COVID-19 testing in hospitals, ports of entry, persons seeking certificates for international travel and in communities were used.

Methods

Proportional age-stratified sampling was used to select 128 specimens. The samples were screened for 33 other respiratory pathogens using the Fast Track Diagnostics multiplex molecular assay.

Results

Overall, 71.1% (n = 91/128) tested positive for at least one respiratory pathogen. Bacterial respiratory pathogens were more predominant (70.3%, n = 90/128) than viral (51.6%, n = 66/128). Staphylococcus aureus was the most prevalent, detected in 22.7% (n = 29/128). The prevalence of influenza was 13.3% (n = 17/128). Rhinovirus had a prevalence of 3.1% (n = 4/128), while it was 10.1% (n = 13/128) for adenovirus. Children, adolescents and the elderly accounted for most influenza-positive specimens, 76.5% (n = 13/17), while 100% (n = 3/3) of specimens positive for Moraxella catarrhalis were from children. All specimens testing positive for Haemophilus influenzae, 100% (n = 5/5) were from children and adolescents. Co-infections were detected in 57.1% (n = 52/91) of specimens testing positive for at least one pathogen.

Conclusion

Bacterial respiratory pathogens appeared to predominate circulation during the COVID-19 pandemic period.

Contribution

Bacterial respiratory pathogens should not be neglected when implementing public health mitigation measures.

Characterising the asynchronous resurgence of common respiratory viruses following the COVID-19 pandemic

The COVID-19 pandemic and relevant non-pharmaceutical interventions (NPIs) interrupted the circulation of common respiratory viruses. These viruses demonstrated an unprecedented asynchronous resurgence as NPIs were relaxed. We compiled a global dataset from a systematic review, online surveillance reports and unpublished data from Respiratory Virus Global Epidemiology Network, encompassing 92 sites. We compared the resurgence timings of respiratory viruses within each site and synthesised differences in timings across sites, using a generalised linear mixed-effects model. We revealed a distinct sequential timing in the first post-pandemic resurgence: rhinovirus resurged the earliest, followed by seasonal coronavirus, parainfluenza virus, respiratory syncytial virus, adenovirus, metapneumovirus and influenza A virus, with influenza B virus exhibiting the latest resurgence. Similar sequential timing was observed in the second resurgence except influenza A virus caught up with metapneumovirus. The consistent asynchrony across geographical regions suggests that virus-specific characteristics, rather than location-specific factors, determining the relative timing of resurgence.

Impact of Viral Co-Detection on the Within-Host Viral Diversity of Influenza Patients

Numerous studies have documented the evidence of virus-virus interactions at the population, host, and cellular levels. However, the impact of these interactions on the within-host diversity of influenza viral populations remains unexplored. Our study identified 13 respiratory viral pathogens from the nasopharyngeal swab samples (NPSs) of influenza-like-illness (ILI) patients during the 2012/13 influenza season using multiplex RT-PCR. Subsequent next-generation sequencing (NGS) of RT-PCR-confirmed influenza A infections revealed all samples as subtype A/H3N2. Out of the 2305 samples tested, 538 (23.3%) were positive for the influenza A virus (IAV), while rhinovirus (RV) and adenoviruses (Adv) were detected in 264 (11.5%) and 44 (1.9%) samples, respectively. Among these, the co-detection of more than one virus was observed in ninety-six samples, and five samples showed co-detections involving more than two viruses. The most frequent viral co-detection was IAV-RV, identified in 48 out of the 96 co-detection cases. Of the total samples, 150 were processed for whole-genome sequencing (WGS), and 132 met the criteria for intra-host single-nucleotide variant (iSNV) calling. Across the genome, 397 unique iSNVs were identified, with most samples containing fewer than five iSNVs at frequencies below 10%. Seven samples had no detectable iSNVs. Notably, the majority of iSNVs (86%) were unique and rarely shared across samples. We conducted a negative binomial regression analysis to examine factors associated with the number of iSNVs detected within hosts. Two age groups-elderly individuals (>64 years old) and school-aged children (6-18 years old)-were significantly associated with higher iSNV counts, with incidence rate ratios (IRR) of 1.80 (95% confidence interval [CI]: 1.09-3.06) and 1.38 (95% CI: 1.01-1.90), respectively. Our findings suggest a minor or negligible contribution of these viral co-detections to the evolution of influenza viruses. However, the data available in this study may not be exhaustive, warranting further, more in-depth investigations to conclusively determine the impact of virus-virus interactions on influenza virus genetic diversity.

Lethal Synergistic Infections by Two Concurrent Respiratory Pathogens

Lethal synergistic infections by concurrent pathogens have occurred in humans, including human immunodeficiency virus and Mycobacterium tuberculosis infections, or in animal or human models of influenza virus, or bacteria, e.g., Streptococcus pneumoniae, concurrent with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the intracellular synergistic interaction possibilities between two respiratory viral pathogens, or between viral and fungal pathogens, merits additional examination. The requirements for synergistic concurrent pathogen infections are: a) relatively little detrimental interference between two pathogens, b) one pathogen having the capability of directly or indirectly assisting the second pathogen by direct immuno-manipulation or indirect provision of infection opportunities and/or metabolic assistance, c) substantial human or environmental prevalence, possibly including a prevalence in any type of health-care facilities or other locations having congregations of potentially infected human or animal vectors and d) substantial transmissibility of the pathogens, which would make their concurrent pathogen infections much more probable. A new definition of pathogen synergy is proposed: "pathogen synergy is an interaction of two or more pathogens during concurrent infections causing an increased infection severity compared to mono-infections by the individual pathogens." Non-respiratory pathogens can also concurrently infect organs besides the lungs. However, the air-transmissible respiratory pathogens, particularly the RNA viruses, can enable highly widespread and synergistic concurrent infections. For instance, certain strains of coronaviruses, influenza viruses and similar respiratory viruses, are highly transmissible and/or widely prevalent in various vectors for transmission to humans and have numerous capabilities for altering lung immune defenses.

Respiratory Pathogen Coinfection During Intersecting COVID-19 and Influenza Epidemics

Respiratory pathogen coinfections pose significant challenges to global public health, particularly regarding the intersecting epidemics of COVID-19 and influenza. This study investigated the incidences of respiratory infectious pathogens in this unique context. We collected throat swab samples from 308 patients with a fever from outpatient and emergency departments at sentinel surveillance hospitals in Xiamen, southeast of China, between April and May 2023, testing for SARS-CoV-2 and 26 other respiratory pathogens. The coinfection rate of the XBB SARS-CoV-2 variant with other respiratory pathogens was higher than that observed during the Alpha and Delta phases. Among patients with influenza, bacterial coinfections were more prevalent. Only 0.65% (2/308) of the patients were concurrently infected with both COVID-19 and influenza. Age-stratified analysis showed a clear pattern, with a higher incidence of coinfections in children under 18 years of age. These findings highlight the need for the timely detection of respiratory pathogen coinfections and for the implementation of appropriate interventions, crucial for reducing disease burden during intersecting respiratory epidemics.

Seasonal Shifts in Influenza, Respiratory Syncytial Virus, and Other Respiratory Viruses After the COVID-19 Pandemic: An Eight-Year Retrospective Study in Jalisco, Mexico

The coronavirus disease 2019 (COVID-19) pandemic profoundly disrupted the epidemiology of respiratory viruses, driven primarily by widespread non-pharmaceutical interventions (NPIs) such as social distancing and masking. This eight-year retrospective study examines the seasonal patterns and incidence of influenza virus, respiratory syncytial virus (RSV), and other respiratory viruses across pre-pandemic, pandemic, and post-pandemic phases in Jalisco, Mexico. Weekly case counts were analyzed using an interrupted time series (ITS) model, segmenting the timeline into these three distinct phases. Significant reductions in respiratory virus circulation were observed during the pandemic, followed by atypical resurgences as NPIs were relaxed. Influenza displayed alternating subtype dominance, with influenza A H3 prevailing in 2022, influenza B surging in 2023, and influenza A H1N1 increasing thereafter, reflecting potential immunity gaps. RSV activity was marked by earlier onset and higher intensity post-pandemic. Other viruses, including human rhinovirus/enterovirus (HRV/HEV) and parainfluenza virus (HPIV), showed altered dynamics, with some failing to return to pre-pandemic seasonality. These findings underscore the need for adaptive surveillance systems and vaccination strategies to address evolving viral patterns. Future research should investigate the long-term public health implications, focusing on vaccination, clinical outcomes, and healthcare preparedness.

Exploring the epidemiological burden of RSV pre- and post-COVID-19 pandemic: A Jordanian tertiary hospital experience

OBJECTIVES

To describe changes in respiratory syncytial virus (RSV) epidemiology, its associated clinical outcomes and predictors of severe acute lower respiratory tract infection (ALRTI) pre- and post-COVID-19.

METHODS

In this retrospective cohort, we analysed data from electronic medical record of children <5 years who were hospitalized at Jordan University Hospital with RSV-associated ALRTI from 2018 to 2022.

RESULTS

325 inpatients with respiratory infections were included. Rate of RSV infections decreased from 74% pre-pandemic to 30% post-pandemic. Patients diagnosed with ALRTI post-COVID had significantly higher SpO2, less chronic disease, lower temperature and respiratory rate at admission and fewer days in hospital compared with those diagnosed pre-COVID. Furthermore, patients diagnosed pre-pandemic were significantly more likely to have abnormal X-rays, used more antibiotics and antivirals, and had higher rates of severe disease than those with infection post-COVID.

CONCLUSION

COVID-19 and its associated social restriction measures led to changes in RSV epidemiology, characterized by a decline in rates and clinical severity in the post-pandemic period. However, further studies are needed to characterize the impact of COVID-19 on subsequent RSV seasons.

Dynamic changes in the circulation of respiratory pathogens in children during and after the containment of the 2019 coronavirus disease pandemic in Kunming, China

PURPOSE

We aimed to determine the changes in the frequency of respiratory pathogens and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during containment of the 2019 coronavirus disease pandemic and elucidate the epidemiological interference that may have occurred after lifting pandemic measures.

METHODS

A total of 4,770 Nasopharyngeal swab samples were collected from children with ARTIs from the First People's Hospital of Yunnan Province between January 2022 and December 2023 and subjected to nucleic acid testing for 13 types of respiratory pathogens and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

RESULTS

The frequency of pathogens among children from 2020 to 2022 was in the following order: HRV > Mp > HADV > H3N2 > HMPV and HRV > HRSV > HPIV > H1N1 > H3N2. In weeks 1 to 3 of 2023, the frequency of pathogens significantly declined, and then H1N1 rebounded significantly in 2023. HRV, HRSV, and H3N2 showed a shift in the season of high frequency. Patterns of multi-pathogen infections were more complex in 2023 than in 2022, with HRV having a higher frequency and co-infection rate than other pathogens. These changes may have been associated with interference caused by the resurgence of SARS-CoV-2 prevalence, in addition to being influenced by changes in pandemic containment and lifting measures.

CONCLUSIONS

The frequency rate of common respiratory pathogens among children was not significantly different and remained high. The study findings help elucidate the aforementioned unique historical period and effectively control respiratory tract infections to reduce the harm to pediatric health caused by respiratory pathogens.

Epidemiological characteristics of respiratory pathogens infections among children after the removal of non-pharmaceutical interventions in central China

BACKGROUND

During the COVID-19 pandemic between 2020 and 2022 in China, various non-pharmaceutical interventions (NPIs) were implemented to reduce the spread of SARS-CoV-2 and other respiratory pathogens. From 2023, China downgraded the management of COVID-19, and compliance with NPIs was no longer mandatory. This study aimed to reveal the epidemiological characteristics of respiratory pathogens in 2023 after the removal of NPIs in central China.

METHODS

Respiratory specimens of children with acute respiratory infections (ARIs) were obtained to detect seven common respiratory pathogens, including influenza A (FluA), influenza B (FluB), adenovirus (ADV), human rhinovirus (HRV), human respiratory syncytial virus (HRSV), human metapneumovirus (HMPV), Mycoplasma pneumoniae (MP). From January 2022 to December 2023, a total of 5423 specimens were collected, including 1122 children in 2022 and 4301 children in 2023.

RESULTS

One or more pathogens were detected in 62.50% specimens in 2023, significantly higher than that in 2022 (44.12%). HRV (13.81%) was the most common pathogen in 2022, whereas MP (24.67%) was predominant in 2023. There was no significant difference in the overall prevalence of HRV, HRSV and HMPV between 2022 and 2023. HRSV was the most common pathogen in the < 1 years children both in 2022 and 2023. However in the ≥ 7 years group, FluB was the predominant pathogen in 2022 whereas MP ranked first in 2023. Co-detection were significantly more frequent in 2023 compared to 2022.

CONCLUSIONS

The removal of NPIs significantly increased the infection rates of the respiratory pathogens among children. Some NPIs, such as wearing mask and hand hygiene are necessary to decrease the prevalence of certain pathogens.

Multisite community-scale monitoring of respiratory and enteric viruses in the effluent of a nursing home and in the inlet of the local wastewater treatment plant

The aim of this study was to evaluate whether community-level monitoring of respiratory and enteric viruses in wastewater can provide a comprehensive picture of local virus circulation. Wastewater samples were collected weekly at the wastewater treatment plant (WWTP) inlet and at the outlet of a nearby nursing home (NH) in Burgundy, France, during the winter period of 2022/2023. We searched for the pepper mild mottle virus as an indicator of fecal content as well as for the main respiratory viruses [severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza, and respiratory syncytial virus] and enteric viruses (rotavirus, sapovirus, norovirus, astrovirus, and adenovirus). Samples were analyzed using real-time reverse transcription PCR-based methods. SARS-CoV-2 was the most frequently detected respiratory virus, with 66.7% of positive samples from the WWTP and 28.6% from the NH. Peaks of SARS-CoV-2 were consistent with the chronological incidence of infections recorded in the sentinel surveillance and the nearby hospital databases. The number of positive samples was lower in the NH than in WWTP for the three respiratory viruses. Enteric viruses were frequently detected, most often sapovirus and norovirus genogroup II, accounting both for 77.8% of positive samples in the WWTP and 57.1% and 37%, respectively, in the NH. The large circulation of sapovirus was unexpected in particular in the NH. Combined wastewater surveillance using simple optimized methods can be a valuable tool for monitoring viral circulation and may serve as a suitable early warning system for identifying both local outbreaks and the onset of epidemics. These results encourage the application of wastewater-based surveillance (WBS) to SARS-CoV2, norovirus, and sapovirus.IMPORTANCEWBS provides valuable information on the spread of epidemic viruses in the environment using appropriate and sensitive detection methods. By monitoring the circulation of viruses using reverse transcription PCR methods in wastewater from the inlet of a wastewater treatment plant and the outlet of a nearby retirement home (connected to the same collective sewer network), we aimed to demonstrate that implementing combined WBS at key community sites allows effective detection of the occurrence of respiratory (influenza, respiratory syncytial virus, and SARS-CoV-2) and enteric (norovirus, rotavirus, and sapovirus) virus infections within a given population. This analysis on a localized scale provided new information on the viral circulation in the two different sites. Implementing WBS to monitor the circulation or the emergence of infectious diseases is an important means of alerting the authorities and improving public health management. WBS could participate actively to the health of humans, animals, and the environment.

Characterizing the interactions between influenza and respiratory syncytial viruses and their implications for epidemic control

Pathogen-pathogen interactions represent a critical but little-understood feature of infectious disease dynamics. In particular, experimental evidence suggests that influenza virus and respiratory syncytial virus (RSV) compete with each other, such that infection with one confers temporary protection against the other. However, such interactions are challenging to study using common epidemiologic methods. Here, we use a mathematical modeling approach, in conjunction with detailed surveillance data from Hong Kong and Canada, to infer the strength and duration of the interaction between influenza and RSV. Based on our estimates, we further utilize our model to evaluate the potential conflicting effects of live attenuated influenza vaccines (LAIV) on RSV burden. We find evidence of a moderate to strong, negative, bidirectional interaction, such that infection with either virus yields 40-100% protection against infection with the other for one to five months. Assuming that LAIV reduces RSV susceptibility in a similar manner, we predict that the impact of such a vaccine at the population level would likely depend greatly on underlying viral circulation patterns. More broadly, we highlight the utility of mathematical models as a tool to characterize pathogen-pathogen interactions.

Seasonality of common respiratory viruses: Analysis of nationwide time-series data

BACKGROUND AND OBJECTIVE

Understanding the seasonal behaviours of respiratory viruses is crucial for preventing infections. We evaluated the seasonality of respiratory viruses using time-series analyses.

METHODS

This study analysed prospectively collected nationwide surveillance data on eight respiratory viruses, gathered from the Korean Influenza and Respiratory Surveillance System. The data were collected on a weekly basis by 52 nationwide primary healthcare institutions between 2015 and 2019. We performed Spearman correlation analyses, similarity analyses via dynamic time warping (DTW) and seasonality analyses using seasonal autoregressive integrated moving average (SARIMA).

RESULTS

The prevalence of rhinovirus (RV, 23.6%-31.4%), adenovirus (AdV, 9.2%-16.6%), human coronavirus (HCoV, 3.0%-6.6%), respiratory syncytial virus (RSV, 11.7%-20.1%), influenza virus (IFV, 11.7%-21.5%), parainfluenza virus (PIV, 9.2%-12.6%), human metapneumovirus (HMPV, 5.6%-6.9%) and human bocavirus (HBoV, 5.0%-6.4%) were derived. Most of them exhibited a high positive correlation in Spearman analyses. In DTW analyses, all virus data from 2015 to 2019, except AdV, exhibited good alignments. In SARIMA, AdV and RV did not show seasonality. Other viruses showed 12-month seasonality. We describe the viruses as winter viruses (HCoV, RSV and IFV), spring/summer viruses (PIV, HBoV), a spring virus (HMPV) and all-year viruses with peak incidences during school periods (RV and AdV).

CONCLUSION

This is the first study to comprehensively analyse the seasonal behaviours of the eight most common respiratory viruses using nationwide, prospectively collected, sentinel surveillance data.

Contribution of Other Respiratory Viruses During Influenza Epidemic Activity in Catalonia, Spain, 2008-2020

BACKGROUND

During seasonal influenza activity, circulation of other respiratory viruses (ORVs) may contribute to the increased disease burden that is attributed to influenza without laboratory confirmation. The objective of this study was to characterize and evaluate the magnitude of this contribution over 12 seasons of influenza using the Acute Respiratory Infection Sentinel Surveillance system in Catalonia (PIDIRAC).

METHODS

A retrospective descriptive study of isolations from respiratory samples obtained by the sentinel surveillance network of physicians was carried out from 2008 to 2020 in Catalonia, Spain. Information was collected on demographic variables (age, sex), influenza vaccination status, epidemic activity weeks each season, and influenza laboratory confirmation.

RESULTS

A total of 12,690 samples were collected, with 46% (5831) collected during peak influenza seasonal epidemic activity. In total, 49.6% of the sampled participants were male and 51.1% were aged <15 years. Of these, 73.7% (4298) of samples were positive for at least one respiratory virus; 79.7% (3425 samples) were positive for the influenza virus (IV), with 3067 samples positive for one IV type, 8 samples showing coinfection with two types of IV, and 350 showing coinfection of IV with more than one virus. The distribution of influenza viruses was 64.2% IVA, 35.2% IVB, and 0.1% IVC. Of the other respiratory viruses identified, there was a high proportion of human rhinovirus (32.3%), followed by human adenovirus (24.3%) and respiratory syncytial virus (18; 7%). Four percent were coinfected with two or more viruses other than influenza. The distribution of coinfections with ORVs and influenza by age groups presents a significant difference in proportions for 0-4, 5-14, 15-64 and >64 (21.5%, 10.8%, 8.2% and 7.6%: p < 0.001). A lower ORVs coinfection ratio was observed in the influenza-vaccinated population (11.9% vs. 17.4% OR: 0.64 IC 95% 0.36-1.14).

CONCLUSIONS

During the weeks of seasonal influenza epidemic activity, other respiratory viruses contribute substantially, either individually or through the coinfection of two or more viruses, to the morbidity attributed to influenza viruses as influenza-like illness (ILI). The contribution of these viruses is especially significant in the pediatric and elderly population. Identifying the epidemiology of most clinically relevant respiratory viruses will aid the development of models of infection and allow for the development of targeted treatments, particularly for populations most vulnerable to respiratory viruses-induced diseases.

The circulating characteristics of common respiratory pathogens in Ningbo, China, both before and following the cessation of COVID-19 containment measures

To assess the circulating characteristics of common respiratory pathogens following the complete relaxation of non-pharmaceutical interventions (NPIs) and the cessation of the dynamic zero-COVID policy. The retrospective analysis was conducted from 14,412 patients with acute respiratory infections (ARIs) from January 24, 2020, to December 31, 2023, including Influenza A virus (IFV-A), Influenza B virus (IFV-B), Respiratory Syncytial Virus (RSV), Human Rhinovirus (HRV), Human Parainfluenza Virus (HPIV), Human Metapneumovirus (HMPV), Human Coronavirus (HCoV), Human Bocavirus (HBoV), Human Adenovirus (HAdV), and Mycoplasma pneumoniae (MP). Compared with 2020-2022, Joinpoint analysis indicated a monthly increase in overall pathogen activity in 2023, rising from an average of 43.05% to an average of 68.46%. The positive rates of IFV-A, IFV-B, HMPV, HPIV, HCoV, and MP increased, while those of HRV and RSV decreased, and no differences in HAdV and HBoV. The outbreak of IFV-A and MP was observed, the positive rate of MP has surpassed pre-COVID-19 pandemic levels and the spread of RSV was interrupted by IFV-A. Infants and toddlers were primarily infected by HRV and RSV, Children and adolescents exhibited a higher prevalence of infections with MP, IFV-A, and HRV, whereas Adults and the elderly were primarily infected by IFV-A. The incidence of co-infections rose from 4.25 to 13.73%. Restricted cubic spline models showed that the susceptible age ranges for multiple pathogens expanded. These changes serve as a reminder to stay alert in the future and offer clinicians a useful guide for diagnosing and treating.

Circulation and Codetections of Influenza Virus, SARS-CoV-2, Respiratory Syncytial Virus, Rhinovirus, Adenovirus, Bocavirus, and Other Respiratory Viruses During 2022-2023 Season in Latvia

This retrospective study analysed the routine data obtained by multiplex real-time RT-qPCR methods for respiratory virus detection. A total of 4814 respiratory specimens collected during 1 September 2022-31 August 2023 were included in the study. A total of 38% of the specimens were positive for at least one target, with the incidence maximum (82%) for the small children (age group 0-4 years). The five dominant virus groups were rhinovirus (RV, 12%), influenza virus A (IAV, 7%), adenovirus (AdV, 6%), respiratory syncytial virus (RSV, 5%), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, 5%). The specimens with multi-detections represented 19% of the positives, unevenly distributed (n = 225, 56, 43, 24) among the age groups 0-4, 5-14, 15-64, and 65< years, respectively. The dominant virus groups in multi-positive specimens were RV (53%), AdV (43%), and bocavirus (BoV, 35%)-in mutual pairs as well as all three together-followed by RSV (21%), and IAV (15%). Our study focused on the specimens with codetections and provides an insight into the variety of the respiratory virus interactions in Latvia during the first year since pandemic-related social restriction measures were eased. The observations also emphasise the need to consider the differentiation between rhinoviruses and enteroviruses, especially for the youngest patients in the age group 0-4.

A complex remodeling of cellular homeostasis distinguishes RSV/SARS-CoV-2 co-infected A549-hACE2 expressing cell lines

Concurrent infections with two or more pathogens with analogous tropism, such as RSV and SARS-CoV-2, may antagonize or facilitate each other, modulating disease outcome. Clinically, discrepancies in the severity of symptoms have been reported in children with RSV/SARS-CoV-2 co-infection. Herein, we propose an in vitro co-infection model to assess how RSV/SARS-CoV-2 co-infection alters cellular homeostasis. To this end, A549-hACE2 expressing cells were either infected with RSV or SARS-CoV-2 alone or co-infected with both viruses. Viral replication was assessed at 72 hours post infection by droplet digital PCR, immunofluorescence, and transmission electron microscopy. Anti-viral/receptor/autophagy gene expression was evaluated by RT-qPCR and confirmed by secretome analyses and intracellular protein production. RSV/SARS-CoV-2 co-infection in A549-hACE2 cells was characterized by: 1) an increase in the replication rate of RSV compared to single infection; 2) an increase in one of the RSV host receptors, ICAM1; 3) an upregulation in the expression/secretion of pro-inflammatory genes; 4) a rise in the number and length of cellular conduits; and 5) augmented autophagosomes formation and/or alteration of the autophagy pathway. These findings suggest that RSV/SARS-CoV-2 co-infection model displays a unique and specific viral and molecular fingerprint and shed light on the viral dynamics during viral infection pathogenesis. This in vitro co-infection model may represent a potential attractive cost-effective approach to mimic both viral dynamics and host cellular responses, providing in future readily measurable targets predictive of co-infection progression.

Seasonality and Co-Detection of Respiratory Viral Infections Among Hospitalised Patients Admitted With Acute Respiratory Illness-Valencia Region, Spain, 2010-2021

BACKGROUND

Respiratory viruses are known to represent a high burden in winter, yet the seasonality of many viruses remains poorly understood. Better knowledge of co-circulation and interaction between viruses is critical to prevention and management. We use > 10-year active surveillance in the Valencia Region to assess seasonality and co-circulation.

METHODS

Over 2010-2021, samples from patients hospitalised for acute respiratory illness were analysed using multiplex real-time PCR to test for 9 viruses: influenza, respiratory syncytial virus (RSV), parainfluenza virus (PIV), rhino/enteroviruses (HRV/ENV), metapneumovirus (MPV), bocavirus, adenovirus, SARS-CoV-2 and non-SARS coronaviruses (HCoV). Winter seasonal patterns of incidence were examined. Instances of co-detection of multiple viruses in a sample were analysed and compared with expected values under a crude model of independent circulation.

RESULTS

Most viruses exhibited consistent patterns between years. Specifically, RSV and influenza seasons were clearly defined, peaking in December-February, as did HCoV and SARS-CoV-2. MPV, PIV and HRV/ENV showed less clear seasonality, with circulation outside the observed period. All viruses circulated in January, suggesting any pair had opportunity for co-infection. Multiple viruses were found in 4% of patients, with more common co-detection in children under 5 (9%) than older ages. Influenza co-detection was generally observed infrequently relative to expectation, while RSV co-detections were more common, particularly among young children.

CONCLUSIONS

We identify characteristic patterns of viruses associated with acute respiratory hospitalisation during winter. Simultaneous circulation permits extensive co-detection of viruses, particularly in young children. However, virus combinations appear to differ in their rates of co-detection, meriting further study.

Molecular epidemiology and vaccine compatibility analysis of seasonal influenza A viruses in the context of COVID-19 epidemic in Wuhan, China

The COVID-19 pandemic had a significant impact on the global influenza vaccination and the epidemics of seasonal influenza. To further explore the molecular epidemiology of influenza viruses and assess vaccine effectiveness, we collected influenza cases in Wuhan during the 2022-2023 influenza season. Among 1312 clinical samples, 312 samples tested positive for influenza viruses using reverse transcription polymerase chain reaction. These positive samples included 146A/H1N1 subtypes (46.8%), 164A/H3N2 subtypes (52.6%) and 2 influenza B virus types (0.6%). Based on the whole genome sequence information of hemagglutinin (HA) and neuraminidase (NA) from 27A/H1N1 influenza virus strains and 26A/H3N2 influenza virus strains obtained in this study, a phylogenetic analysis was conducted. The analysis revealed that all A/H1N1 strains belonged to the evolutionary branch 6B.1A.5a.2a, and they exhibited specific substitutions at positions K71Q, Q206E, E241A, and R276K. Similarly, all A/H3N2 strains were classified into the 3C.2a1b.2a.1a subclade and displayed amino acid substitutions at positions S172H, N175Y, I176T, K187N, and S214P. Notably, the A/H3N2 strains also acquired a new potential glycosylation site at position N174. Using an epitope model, the predicted vaccine effectiveness was assessed for the A/H1N1 and A/H3N2 strains. The predicted vaccine effectiveness against the Wuhan influenza epidemic strain was over 85% for the A/H1N1 vaccine strain. However, the effectiveness against the A/H3N2 vaccine strain was only 48.7%. To further verify the protection of influenza vaccine against circulating influenza viruses in the region, we conducted in vivo and in vitro animal studies. The results of in vitro neutralization experiment showed that rabbit serum antibodies inoculated with quadrivalent isolated influenza vaccine had neutralization ability against all 24 isolated influenza viruses. In vivo experiments showed that vaccinated mice had fewer lung lesions when infected with the influenza strain circulating in Wuhan, suggesting that vaccination can effectively reduce the occurrence of severe lung damage. These findings emphasize the importance of accurately predicting seasonal influenza strains for effective influenza prevention and control, especially during the co-circulation of SARS-CoV-2 and influenza viruses. This study provides valuable information on the seasonal influenza virus in Wuhan during the COVID-19 pandemic and serves as a basis for vaccine prediction and updates.

Spatio-temporal modeling of co-dynamics of smallpox, measles, and pertussis in pre-healthcare Finland

Infections are known to interact as previous infections may have an effect on risk of succumbing to a new infection. The co-dynamics can be mediated by immunosuppression or modulation, shared environmental or climatic drivers, or competition for susceptible hosts. Research and statistical methods in epidemiology often concentrate on large pooled datasets, or high quality data from cities, leaving rural areas underrepresented in literature. Data considering rural populations are typically sparse and scarce, especially in the case of historical data sources, which may introduce considerable methodological challenges. In order to overcome many obstacles due to such data, we present a general Bayesian spatio-temporal model for disease co-dynamics. Applying the proposed model on historical (1820-1850) Finnish parish register data, we study the spread of infectious diseases in pre-healthcare Finland. We observe that measles, pertussis, and smallpox exhibit positively correlated dynamics, which could be attributed to immunosuppressive effects or, for example, the general weakening of the population due to recurring infections or poor nutritional conditions.

SARS-CoV-2 co-detection with other respiratory pathogens-descriptive epidemiological study

BACKGROUND

Co-detection of respiratory pathogens with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is poorly understood. This descriptive epidemiological study aimed to determine the effect of the interaction of different respiratory pathogens on clinical variables.

METHODS

We retrospectively reviewed the results of comprehensive multiplex polymerase chain reaction (PCR) testing from November 2020 to March 2023 to estimate respiratory pathogen co-detection rates in Shinjuku, Tokyo. We evaluated the interactions of respiratory pathogens, particularly SARS-CoV-2, between observed and expected co-detection. We estimated the trend of co-detection with SARS-CoV-2 in terms of age and sex and applied a multiple logistic regression model adjusted for age, testing period, and sex to identify influencing factors between co-detection and single detection for each pathogen.

RESULTS

Among 57,746 patients who underwent multiplex PCR testing, 10,516 (18.2%) had positive for at least one of the 22 pathogens. Additionally, 881 (1.5%) patients were confirmed to have a co-detection. SARS-CoV-2 exhibited negative interactions with adenovirus, coronavirus, human metapneumovirus, parainfluenza virus, respiratory syncytial virus, and rhino/enterovirus. SARS-CoV-2 co-detection with other pathogens occurred most frequently in patients of the youngest age group (0-4 years). A multiple logistic regression model indicated that younger age was the most influential factor for SARS-CoV-2 co-detection with other respiratory pathogens.

CONCLUSION

The study highlights the prevalence of SARS-CoV-2 co-detection with other respiratory pathogens in younger age groups, necessitating further exploration of the clinical implications and severity of SARS-CoV-2 co-detection.

Severe Respiratory Syncytial Virus Infections in Elderly Persons During the COVID-19 Pandemic

Background

Respiratory syncytial virus (RSV) is a pathogenic respiratory virus that is considered to affect not only children but also adults, especially elderly persons aged ≥65 years. However, in Japan, the annual epidemic situation and severity of RSV infections in these adults have not yet been clarified, especially during the COVID-19 pandemic.

Methods

The epidemic of RSV, especially the number of adults with RSV infection during the COVID-19 period, was retrospectively analyzed. In addition, the clinical features of patients aged ≥65 years (older group) and those aged ≤64 years (younger group) were compared.

Results

A total of 58 patients were found to have RSV infections from April to August 2021. Ten were adults, and five each were detected in June and July, respectively. Of the 10 adult patients, three were in the older group and were more often infected by their grandchildren, and seven were in the younger group. All older patients had underlying diseases, including diabetes mellitus. In addition, the older group showed more severe inflammation, such as increased white blood cell counts and C-reactive protein levels, and received antibiotic therapy, whereas no antibiotics were used for the younger group. Two of the three older patients were admitted to our hospital, but survived.

Conclusion

These data suggest that RSV infection in adult patients was related to the increase in pediatric RSV patients and that the infection season had shifted to summer, similar to other countries. Among the adult RSV patients, those aged ≥65 years were more often infected by their grandchildren and received antibiotics because of their more severe inflammatory status than patients aged ≤64 years during the COVID-19 pandemic in Japan.

Simultaneous and ultrafast detection of pan-SARS-coronaviruses and influenza A/B viruses by a novel multiplex real-time RT-PCR assay

Here we report an ultrafast quadruplex RT-qPCR assay with robust diagnostic ability to detect and distinguish pan-SARS-CoVs and influenza A/B viruses within 35 min. This quadruplex RT-qPCR assay comprised of one novel RNA-based internal control targeting human β2-microglobulin (B2M) for process accuracy and three newly-designed primers-probe sets targeting the envelope protein (E) of pan-SARS-CoV, matrix protein (MP) of influenza A virus and non-structural (NS) region of influenza B virus. This quadruplex assay exhibited a sensitivity comparable to its singleplex counterparts and a slightly higher to that of the Centers for Disease Control and Prevention-recommended SARS-CoV-2 and influenza A/B assays. The novel assay showed no false-positive amplifications with other common respiratory viruses, and its 95 % limits of detection for pan-SARS-CoV and influenza A/B virus was 4.26-4.52 copies/reaction. Moreover, the assay was reproducible with less than 1 % coefficient of variation and adaptable testing different clinical and environmental samples. Our ultrafast quadruplex RT-qPCR assay can serve as an attractive tool for effective differentiation of influenza A/B virus and SARS-CoV-2, but more importantly prognose the reemergence/emergence of SARS and novel coronaviruses or influenza viruses from animal spillover.

COVID-19 pandemic-altered epidemiology of respiratory syncytial virus and human metapneumovirus infections in young children

To evaluate the impact of the COVID-19 pandemic on the epidemiology of respiratory viral infections, we examined the prevalence of respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) infections for pediatric patients admitted to our hospital before and after the COVID-19 pandemic from January 2015 to June 2023. During the COVID-19 pandemic, no outbreaks of RSV infections were seen in 2020, and no outbreaks of hMPV infections were seen in 2020 and 2021. Before the pandemic, the two epidemics did not overlap, but after the pandemic, the two epidemics almost overlapped for the second year in a row. The average age of patients with both RSV and hMPV infection after the pandemic was significantly older than before the pandemic by approximately one year.

In silico molecular screening of bioactive natural compounds of rosemary essential oil and extracts for pharmacological potentials against rhinoviruses

Rhinoviruses (RVs) cause upper respiratory tract infections and pneumonia in children and adults. These non-enveloped viruses contain viral coats of four capsid proteins: VP1, VP2, VP3, and VP4. The canyon on VP1 used cell surface receptor ICAM-1 as the site of attachment and for the internalization of viruses. To date, there has been no drug or vaccine available against RVs. In this study, bioactive natural compounds of rosemary (Salvia rosmarinus L.), which are known for their pharmacological potential, were considered to target the VP1 protein. A total of 30 bioactive natural compounds of rosemary were taken as ligands to target viral proteins. The PkCSM tool was used to detect their adherence to Lipinski's rule of five and the ADMET properties of the selected ligands. Further, the CB-Dock tool was used for molecular docking studies between the VP1 protein and ligands. Based on the molecular docking and ADMET profiling results, phenethyl amine (4 methoxy benzyl) was selected as the lead compound. A comparative study was performed between the lead compound and two antiviral drugs, Placonaril and Nitazoxanide, to investigate the higher potential of natural compounds over synthetic drugs. Placonaril also targets VP1 but failed in clinical trials while Nitazoxanide was examined in clinical trials against rhinoviruses. It was discovered from this study that the (4 methoxy benzyl) phenethyl amine exhibited less toxicity in comparison to other tested drugs against RVs. More research is needed to determine its potential and make it a good medication against RVs.

Considerations for viral co-infection studies in human populations

When respiratory viruses co-circulate in a population, individuals may be infected with multiple pathogens and experience possible virus-virus interactions, where concurrent or recent prior infection with one virus affects the infection process of another virus. While experimental studies have provided convincing evidence for within-host mechanisms of virus-virus interactions, evaluating evidence for viral interference or potentiation using population-level data has proven more difficult. Recent studies have quantified the prevalence of co-detections using populations drawn from clinical settings. Here, we focus on selection bias issues associated with this study design. We provide a quantitative account of the conditions under which selection bias arises in these studies, review previous attempts to address this bias, and propose unbiased study designs with sample size estimates needed to ascertain viral interference. We show that selection bias is expected in cross-sectional co-detection prevalence studies conducted in clinical settings, except under a strict set of assumptions regarding the relative probabilities of being included in a study limited to individuals with clinical disease under different viral states. Population-wide studies that collect samples from participants irrespective of their clinical status would meanwhile require large sample sizes to be sufficiently powered to detect viral interference, suggesting that a study's timing, inclusion criteria, and the expected magnitude of interference are instrumental in determining feasibility.

Temporal trends in respiratory pathogens following the COVID-19 pandemic and climate variables: A unicentric retrospective evaluation of 24 pathogens in a temperate subtropical region

Temperature and humidity are studied in the context of seasonal infections in temperate and tropical zones, but the relationship between viral trends and climate variables in temperate subtropical zones remains underexplored. Our retrospective study analyzes respiratory pathogen incidence and its correlation with climate data in a subtropical zone. Retrospective observational study at Moinhos de Vento Hospital, South Brazil, aiming to assess seasonal trends in respiratory pathogens, correlating them with climate data. The study included patients of all ages from various healthcare settings, with data collected between April 2022 and July 2023. Biological samples were analyzed for 24 pathogens using polymerase chain reaction and hybridization techniques; demographic variables were also collected. The data was analyzed descriptively and graphically. Spearman tests and Poisson regression were used as correlation tests. Tests were clustered according to all pathogens, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza viruses, rhinovirus, and respiratory syncytial virus (RSV). Between April 2022 and July 2023, 3329 tests showed a 71.6% positivity rate. Rhinovirus and RSV predominated, exhibiting seasonal patterns. Temperature was inversely correlated with the viruses, notably rhinovirus, but SARS-CoV-2 was positively correlated. Air humidity was positively correlated with all pathogens, RSV, rhinovirus, and atmospheric pressure with all pathogens and rhinovirus. Our results showed statistically significant correlations, with modest effect sizes. Our study did not evaluate causation effects. Despite the correlation between climate and respiratory pathogens, our work suggests additional factors influencing transmission dynamics. Our findings underscore the complex interplay between climate and respiratory infections in subtropical climates.

Viral interference between severe acute respiratory syndrome coronavirus 2 and influenza A viruses

Some respiratory viruses can cause a viral interference through the activation of the interferon (IFN) pathway that reduces the replication of another virus. Epidemiological studies of coinfections between SARS-CoV-2 and other respiratory viruses have been hampered by non-pharmacological measures applied to mitigate the spread of SARS-CoV-2 during the COVID-19 pandemic. With the ease of these interventions, SARS-CoV-2 and influenza A viruses can now co-circulate. It is thus of prime importance to characterize their interactions. In this work, we investigated viral interference effects between an Omicron variant and a contemporary influenza A/H3N2 strain, in comparison with an ancestral SARS-CoV-2 strain and the 2009 pandemic influenza A/H1N1 virus. We infected nasal human airway epitheliums with SARS-CoV-2 and influenza, either simultaneously or 24 h apart. Viral load was measured by RT-qPCR and IFN-α/β/λ1/λ2 proteins were quantified by immunoassay. Expression of four interferon-stimulated genes (ISGs; OAS1/IFITM3/ISG15/MxA) was also measured by RT-droplet digital PCR. Additionally, susceptibility of each virus to IFN-α/β/λ2 recombinant proteins was determined. Our results showed that influenza A, and especially A/H3N2, interfered with both SARS-CoV-2 viruses, but that SARS-CoV-2 did not significantly interfere with A/H3N2 or A/H1N1. Consistently with these results, influenza, and particularly the A/H3N2 strain, caused a higher production of IFN proteins and expression of ISGs than SARS-CoV-2. SARS-CoV-2 induced a marginal IFN production and reduced the IFN response during coinfections with influenza. All viruses were susceptible to exogenous IFNs, with the ancestral SARS-CoV-2 and Omicron being less susceptible to type I and type III IFNs, respectively. Thus, influenza A causes a viral interference towards SARS-CoV-2 most likely through an IFN response. The opposite is not necessarily true, and a concurrent infection with both viruses leads to a lower IFN response. Taken together, these results help us to understand how SARS-CoV-2 interacts with another major respiratory pathogen.

Competition to Explain Stable Prevalence of Seasonal Viral Respiratory Infections in Temperate Climates

The prevalence of seasonal viral respiratory infections in temperate climates is relatively stable, but individual viruses vary. This phenomenon is not explained via the conventional view of influenza seasonality which is still incomplete. The viral-flow theory, an outsider theory about the seasonality of influenza, where insects buffer viruses, is able to explain the stable prevalence of viral respiratory infections. Alternative hypotheses to explain this phenomenon are discussed.

Ten-year retrospective data analysis reveals frequent respiratory co-infections in hospitalized patients in Augsburg

Clinical data on the types of respiratory pathogens which are most frequently engaged in respiratory co-infections of children and adults are lacking. We analyzed 10 years of data on a total of over 15,000 tests for 16 viral and bacterial pathogens detected in clinical samples at the University Hospital of Augsburg, Germany. Co-infection frequencies and their seasonal patterns were examined using a proportional distribution model. Co-infections were detected in 7.3% of samples, with a higher incidence in children and males. The incidence of interbacterial and interviral co-infections was higher than expected, whereas bacterial-viral co-infections were less frequent. H. influenzae, S. pneumoniae, rhinovirus, and respiratory syncytial virus (RSV) were most frequently involved. Most co-infections occurred in winter, but distinct summer peaks were also observed, which occurred even in children, albeit less pronounced than in adults. Seasonality of respiratory (co-)infections decreased with age. Our results suggest to adjust existing testing strategies during high-incidence periods.

Sentinel Enhanced Dengue Surveillance System - Puerto Rico, 2012-2022

Problem/Condition

Dengue is the most prevalent mosquitoborne viral illness worldwide and is endemic in Puerto Rico. Dengue's clinical spectrum can range from mild, undifferentiated febrile illness to hemorrhagic manifestations, shock, multiorgan failure, and death in severe cases. The disease presentation is nonspecific; therefore, various other illnesses (e.g., arboviral and respiratory pathogens) can cause similar clinical symptoms. Enhanced surveillance is necessary to determine disease prevalence, to characterize the epidemiology of severe disease, and to evaluate diagnostic and treatment practices to improve patient outcomes. The Sentinel Enhanced Dengue Surveillance System (SEDSS) was established to monitor trends of dengue and dengue-like acute febrile illnesses (AFIs), characterize the clinical course of disease, and serve as an early warning system for viral infections with epidemic potential.

Reporting Period

May 2012-December 2022.

Description of System

SEDSS conducts enhanced surveillance for dengue and other relevant AFIs in Puerto Rico. This report includes aggregated data collected from May 2012 through December 2022. SEDSS was launched in May 2012 with patients with AFIs from five health care facilities enrolled. The facilities included two emergency departments in tertiary acute care hospitals in the San Juan-Caguas-Guaynabo metropolitan area and Ponce, two secondary acute care hospitals in Carolina and Guayama, and one outpatient acute care clinic in Ponce. Patients arriving at any SEDSS site were eligible for enrollment if they reported having fever within the past 7 days. During the Zika epidemic (June 2016-June 2018), patients were eligible for enrollment if they had either rash and conjunctivitis, rash and arthralgia, or fever. Eligibility was expanded in April 2020 to include reported cough or shortness of breath within the past 14 days. Blood, urine, nasopharyngeal, and oropharyngeal specimens were collected at enrollment from all participants who consented. Diagnostic testing for dengue virus (DENV) serotypes 1-4, chikungunya virus, Zika virus, influenza A and B viruses, SARS-CoV-2, and five other respiratory viruses was performed by the CDC laboratory in San Juan.

Results

During May 2012-December 2022, a total of 43,608 participants with diagnosed AFI were enrolled in SEDSS; a majority of participants (45.0%) were from Ponce. During the surveillance period, there were 1,432 confirmed or probable cases of dengue, 2,293 confirmed or probable cases of chikungunya, and 1,918 confirmed or probable cases of Zika. The epidemic curves of the three arboviruses indicate dengue is endemic; outbreaks of chikungunya and Zika were sporadic, with case counts peaking in late 2014 and 2016, respectively. The majority of commonly identified respiratory pathogens were influenza A virus (3,756), SARS-CoV-2 (1,586), human adenovirus (1,550), respiratory syncytial virus (1,489), influenza B virus (1,430), and human parainfluenza virus type 1 or 3 (1,401). A total of 5,502 participants had confirmed or probable arbovirus infection, 11,922 had confirmed respiratory virus infection, and 26,503 had AFI without any of the arboviruses or respiratory viruses examined.

Interpretation

Dengue is endemic in Puerto Rico; however, incidence rates varied widely during the reporting period, with the last notable outbreak occurring during 2012-2013. DENV-1 was the predominant virus during the surveillance period; sporadic cases of DENV-4 also were reported. Puerto Rico experienced large outbreaks of chikungunya that peaked in 2014 and of Zika that peaked in 2016; few cases of both viruses have been reported since. Influenza A and respiratory syncytial virus seasonality patterns are distinct, with respiratory syncytial virus incidence typically reaching its annual peak a few weeks before influenza A. The emergence of SARS-CoV-2 led to a reduction in the circulation of other acute respiratory viruses.

Public Health Action

SEDSS is the only site-based enhanced surveillance system designed to gather information on AFI cases in Puerto Rico. This report illustrates that SEDSS can be adapted to detect dengue, Zika, chikungunya, COVID-19, and influenza outbreaks, along with other seasonal acute respiratory viruses, underscoring the importance of recognizing signs and symptoms of relevant diseases and understanding transmission dynamics among these viruses. This report also describes fluctuations in disease incidence, highlighting the value of active surveillance, testing for a panel of acute respiratory viruses, and the importance of flexible and responsive surveillance systems in addressing evolving public health challenges. Various vector control strategies and vaccines are being considered or implemented in Puerto Rico, and data from ongoing trials and SEDSS might be integrated to better understand epidemiologic factors underlying transmission and risk mitigation approaches. Data from SEDSS might guide sampling strategies and implementation of future trials to prevent arbovirus transmission, particularly during the expansion of SEDSS throughout the island to improve geographic representation.

Sequential Infection with Influenza A Virus Followed by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Leads to More Severe Disease and Encephalitis in a Mouse Model of COVID-19

COVID-19 is a spectrum of clinical symptoms in humans caused by infection with SARS-CoV-2. The coalescence of SARS-CoV-2 with seasonal respiratory viruses, particularly influenza viruses, is a global health concern. To understand this, transgenic mice expressing the human ACE2 receptor (K18-hACE2) were infected with influenza A virus (IAV) followed by SARS-CoV-2 and the host response and effect on virus biology was compared to K18-hACE2 mice infected with IAV or SARS-CoV-2 alone. The sequentially infected mice showed reduced SARS-CoV-2 RNA synthesis, yet exhibited more rapid weight loss, more severe lung damage and a prolongation of the innate response compared to the singly infected or control mice. Sequential infection also exacerbated the extrapulmonary encephalitic manifestations associated with SARS-CoV-2 infection. Conversely, prior infection with a commercially available, multivalent live-attenuated influenza vaccine (Fluenz Tetra) elicited the same reduction in SARS-CoV-2 RNA synthesis, albeit without the associated increase in disease severity. This suggests that the innate immune response stimulated by IAV inhibits SARS-CoV-2. Interestingly, infection with an attenuated, apathogenic influenza vaccine does not result in an aberrant immune response and enhanced disease severity. Taken together, the data suggest coinfection ('twinfection') is deleterious and mitigation steps should be instituted as part of the comprehensive public health and management strategy of COVID-19.