The Clinical and Economic Burden of Norovirus Gastroenteritis in the United States

Optimization of the 5-plex digital PCR workflow for simultaneous monitoring of SARS-CoV-2 and other pathogenic viruses in wastewater

Wastewater-based epidemiology is a valuable tool for monitoring pathogenic viruses in the environment, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19). While quantitative polymerase chain reaction (qPCR) is widely used for pathogen surveillance in wastewater, it can be affected by inhibition and is limited to relative quantification. Digital PCR (dPCR) offers potential solutions to these limitations. In this study, a 5-plex dPCR workflow was optimized for the simultaneous detection of SARS-CoV-2, influenza A virus, enteroviruses (EnV), and noroviruses of genogroups I (NoV-GI) and GII (NoV-GII) in wastewater samples. Wastewater samples (n = 36) were collected from a wastewater treatment plant in Japan between August and October 2022. The optimization included the evaluation of singleplex and 5-plex dPCR assays, and two different concentration methods, extraction kits, and dPCR approaches. The performance of singleplex and 5-plex dPCR assays showed comparable linearity and reliability, with the 5-plex assays showing greater efficiency. The polyethylene glycol (PEG) precipitation method showed better performance over the centrifugation method, two-step reverse transcription (RT)-dPCR over the one-step RT-dPCR, and AllPrep PowerViral DNA/RNA Kit showed better performance than the QIAamp Viral RNA Mini Kit. The optimal workflow therefore included PEG precipitation, the AllPrep PowerViral DNA/RNA Kit, and two-step RT-dPCR. This workflow was selected to monitor the presence of SARS-CoV-2 and other pathogenic viruses in wastewater samples in a 5-plex dPCR approach, yielding promising results. SARS-CoV-2 RNA was detected in the majority of samples, with NoV-GI, NoV-GII, and EnV also being detected. The successful optimization and application of the 5-plex dPCR assay for pathogen surveillance in wastewater offers significant benefits, including enhanced community health assessment and more effective responses to public health threats.

Childcare and School Acute Gastroenteritis Outbreaks: 2009-2020

OBJECTIVES

Acute gastroenteritis (AGE) outbreaks commonly occur in congregate settings, including schools and childcare facilities. These outbreaks disrupt institutions, causing absences and temporary facility closures. This study analyzed the epidemiology of school and childcare AGE outbreaks in the United States.

METHODS

We analyzed AGE outbreaks occurring in kindergarten to grade 12 schools and childcare facilities reported via the National Outbreak Reporting System in the United States from 2009 to 2019 and compared this information to 2020 data. Outbreak and case characteristics were compared using the Kruskal-Wallis rank sum test, χ2 goodness-of-fit test, and Fisher exact test.

RESULTS

From 2009 to 2019, there were 2623 school, 1972 childcare, and 38 school and childcare outbreaks. School outbreaks were larger (median, 29 cases) than childcare outbreaks (median, 10 cases). Childcare outbreaks were longer (median, 15 days) than school outbreaks (median, 9 days). Norovirus (2383 outbreaks; 110 190 illnesses) and Shigella spp. (756 outbreaks; 9123 illnesses) were the most reported etiologies. Norovirus was the leading etiology in schools; norovirus and Shigella spp. were dominant etiologies in childcare centers. Most (85.7%) outbreaks were spread via person-to-person contact. In 2020, 123 outbreaks were reported, 85% in the first quarter.

CONCLUSIONS

Schools and childcare centers are common AGE outbreak settings in the United States. Most outbreaks were caused by norovirus and Shigella spp. and spread via person-to-person transmission. Fewer outbreaks were reported in 2020 from the COVID-19 pandemic. Prevention and control efforts should focus on interrupting transmission, including environmental disinfection, proper handwashing, safe diapering, and exclusion of ill persons.

Epidemiology of Norovirus in the First 2 Years of Life in an Australian Community-based Birth Cohort

BACKGROUND

Noroviruses are a leading cause of acute gastroenteritis across all age groups in Australia. We explored the epidemiology of symptomatic and asymptomatic norovirus infection and assessed risk factors and the related healthcare burden in Australian children during their first 2 years of life.

METHODS

Participants in the Observational Research in Childhood Infectious Diseases birth cohort provided weekly stool swabs, daily gastrointestinal symptoms (vomiting and loose stools) observations and healthcare data. Swabs were batch-tested for norovirus genogroups (GI and GII) using real-time polymerase chain reaction assays.

RESULTS

Overall, 158 children returned 11,124 swabs. There were 221 infection episodes, of which 183 (82.8%) were GII. The incidence rate was 0.90 infections per child-year [95% confidence interval (CI): 0.74-1.09]. The symptomatic infection incidence rate was 0.39 per child-year (95% CI: 0.31-0.48), peaking between ages 6 and 11 months [0.58 (95% CI: 0.41-0.81)]. Incidence increased significantly with age and childcare attendance. Of 209 episodes with symptom diary data, 82 (39.2%) were symptomatic; of these 70 (85.4%) were associated with vomiting and 29 (35.4%) with diarrhea. Forty-one percent of symptomatic episodes required healthcare, including 4 emergency department presentations and 1 hospitalization. Children with initial infections had almost twice the risk of seeking primary healthcare compared to subsequent infections (adjusted risk ratio 1.92; 95% CI: 1.01-3.65).

CONCLUSIONS

Norovirus infections, particularly GII, are common in Australian children 6-23 months of age. Estimates of norovirus incidence, including symptomatic infections and healthcare utilization in community settings in young children, are crucial for planning norovirus vaccine programs and determining vaccine effectiveness.

Viable Norovirus Persistence in Water Microcosms

Human noroviruses are one of the leading causes of acute gastroenteritis worldwide. Based on quantitative microbial risk assessments, norovirus contributes the greatest infectious risk of any pathogen from exposure to sewage-contaminated water; however, these estimates have been based upon molecular (i.e., RNA-based) data as human norovirus has remained largely unculturable in the laboratory. Current approaches to assess the environmental fate of noroviruses rely on the use of culturable surrogate viruses and molecular methods. Human intestinal enteroids (HIEs) are an emerging cell culture system capable of amplifying viable norovirus. Here, we applied the HIE assay to assess both viable norovirus and norovirus RNA persistence in surface, tap, and deionized water microcosms. Viable norovirus decreased to below the detection limit in tap and deionized water microcosms and was measured in a single replicate in the surface water microcosm at study conclusion (28 days). Conversely, the norovirus RNA signal remained constant over the duration of the study, even when viable norovirus was below the limit of detection. Our findings demonstrate the disconnect between current environmental norovirus detection via molecular methods and viability as assessed through the HIE assay. These results imply that molecular norovirus monitoring is not inherently representative of infectious norovirus.

Cancer systems epidemiology: Overcoming misconceptions and integrating systems approaches into cancer research

Patricia Mabry and coauthors discuss application of systems approaches in cancer research.

Immunogenicity of a bivalent virus-like particle norovirus vaccine in children from 1 to 8 years of age: A phase 2 randomized, double-blind study

BACKGROUND

Young children can suffer severe consequences of norovirus gastroenteritis. We performed a dose-finding study of a bivalent virus-like particle (VLP) vaccine candidate (TAK-214) in healthy 1-8-year-old children.

METHODS

In this phase 2 study two age cohorts (1-3 and 4-8 years of age inclusive, N = 120 per cohort) of children enrolled from Finland, Panama and Colombia were initially randomized 1:1:1:1 to four groups which were further split into two equal subgroups, to receive one or two intramuscular doses of four TAK-214 formulations containing 15/15, 15/50, 50/50 or 50/150 μg of GI.1/GII.4c genotype VLPs and 0.5 mg Al(OH)₃ at 28 days interval. ELISA Pan-Ig and histoblood group antigen-blocking (HBGA) antibodies against each VLP were measured on days 1, 29, 57 and 210. Parents/guardians recorded solicited local and systemic adverse events (AE) and any unsolicited or serious AEs (SAE).

RESULTS

All formulations were well-tolerated across both age cohorts and dosage groups with no vaccine-related SAEs reported. Solicited AEs were mostly mild-to-moderate, resolved quickly, and did not increase after the second dose. Pan-Ig and HBGA responses induced after one dose were only slightly increased by the second dose. Across dose groups at Day 29 after one dose GI.1 Pan Ig seroresponse rates (SRR) were 82-97% and 81-96% and GII.4c SRR were 79-97% and 80-91% in 1-3 and 4-8 year-olds, respectively. Respective rates were to 92-93% and 73-92% for GI.1, and 77-100% and 62-83% for GII.4c at Day 57 following two doses. HBGA responses had similar profiles. Both Pan Ig and HBGA geometric mean titers persisted above baseline up to Day 210.

CONCLUSIONS

All dosages of TAK-214 displayed acceptable reactogenicity in 1-8-year-old children and induced robust, durable immune responses after one dose which are further increased after two doses.

Recent Developments in Isothermal Amplification Methods for the Detection of Foodborne Viruses

Foodborne and enteric viruses continue to impose a significant public health and economic burden globally. As many of these viruses are highly transmissible, the ability to detect them portably, sensitively, and rapidly is critical to reduce their spread. Although still considered a gold standard for detection of these viruses, real time polymerase chain reaction (PCR)-based technologies have limitations such as limited portability, need for extensive sample processing/extraction, and long time to result. In particular, the limitations related to the susceptibility of real time PCR methods to potential inhibitory substances present in food and environmental samples is a continuing challenge, as the need for extensive nucleic acid purification prior to their use compromises the portability and rapidity of such methods. Isothermal amplification methods have been the subject of much investigation for these viruses, as these techniques have been found to be comparable to or better than established PCR-based methods in portability, sensitivity, specificity, rapidity, and simplicity of sample processing. The purpose of this review is to survey and compare reports of these isothermal amplification methods developed for foodborne and enteric viruses, with a special focus on the performance of these methods in the presence of complex matrices.

Is the Medium Still the Message? Culture-Independent Diagnosis of Gastrointestinal Infections

Infectious diarrhea is caused by a variety of pathogens, including viruses, bacteria, and parasitic organisms. Though the causative agent of diarrhea has historically been evaluated via stool cultures, recently, culture-independent diagnostic tests (CIDT) have been developed and utilized with increasing frequency. Current practice guidelines recommend their use as adjuncts to stool cultures for diagnosing acute and chronic diarrhea. The three principal CIDT are microscopy, enzyme-based immunoassays (EIAs), and molecular based polymerase chain reaction (PCR). This review explores the common causes of infectious diarrhea, the basics of stool culture, the diagnostic utility of these three culture-independent modalities, and the strengths and weaknesses of all currently available clinical techniques. It also outlines considerations for specific populations including returning travelers and those with inflammatory bowel disease.

Serological Humoral Immunity Following Natural Infection of Children with High Burden Gastrointestinal Viruses

Acute gastroenteritis (AGE) is a major cause of morbidity and mortality worldwide, resulting in an estimated 440,571 deaths of children under age 5 annually. Rotavirus, norovirus, and sapovirus are leading causes of childhood AGE. A successful rotavirus vaccine has reduced rotavirus hospitalizations by more than 50%. Using rotavirus as a guide, elucidating the determinants, breath, and duration of serological antibody immunity to AGE viruses, as well as host genetic factors that define susceptibility is essential for informing development of future vaccines and improving current vaccine candidates. Here, we summarize the current knowledge of disease burden and serological antibody immunity following natural infection to inform further vaccine development for these three high-burden viruses.

Cost of Hospitalizations for Leading Foodborne Pathogens in the United States: Identification by International Classification of Disease Coding and Variation by Pathogen

Foodborne illness is a continuing public health problem in the United States. Seven pathogens-Campylobacter, Clostridium perfringens, Shiga toxin-producing Escherichia coli O157, Listeria monocytogenes, nontyphoidal Salmonella, norovirus, and Toxoplasma gondii-are estimated to cause >90% of the foodborne illnesses, hospitalizations, and deaths attributed to 31 known pathogens. The purpose of this article was to inform estimates of the cost of hospitalizations associated with these pathogens using National Inpatient Survey data from January 2012 through September 2015. The article explored two methodological issues. First, is it more appropriate to use hospitalizations identified using principal or all diagnosis codes when estimating cost? Second, should pathogen-specific or overall mean cost estimates be used? After excluding C. perfringens because of low sample size, the remaining six pathogens included in the analysis were associated with 17,102 hospital discharge records. Of these 55% have the pathogen listed as a principal diagnosis (FBP-PD), ranging from 6% for T. gondii to 68% for nontyphoidal Salmonella. The mean per-case cost of records with the pathogen listed as a secondary diagnosis (FBP-SD) was 2.7 times higher than FBP-PD. FBP-SD were also more severe than FBP-PD with longer lengths of stay, increasing loss of function, and increasing risk of mortality. Severity was the main driver of cost. We also found severity of illness and cost of hospitalizations vary by pathogen. Based on identifying cases with a pathogen in either FBP-PD or FBP-SD, we found mean per-case hospitalization cost across the six pathogens included in this study was $17,515, ranging from $11,552 for Campylobacter to $34,206 for norovirus. In summary, if only FBP-PD cases were used to estimate cost, estimates would likely underestimate hospitalization costs among those cases with a pathogen-specific diagnosis. Because these foodborne pathogens varied in severity of illness, the mean cost of hospitalizations also varied significantly by pathogen.

Simvastatin Reduces Protection and Intestinal T Cell Responses Induced by a Norovirus P Particle Vaccine in Gnotobiotic Pigs

Noroviruses (NoVs) are a leading cause of acute gastroenteritis worldwide. P particles are a potential vaccine candidate against NoV. Simvastatin is a cholesterol-reducing drug that is known to increase NoV infectivity. In this study, we examined simvastatin’s effects on P particle-induced protective efficacy and T-cell immunogenicity using the gnotobiotic pig model of human NoV infection and diarrhea. Pigs were intranasally inoculated with three doses (100 µg/dose) of GII.4/VA387-derived P particles together with monophosphoryl lipid A and chitosan adjuvants. Simvastatin-fed pigs received 8 mg/day orally for 11 days prior to challenge. A subset of pigs was orally challenged with 10 ID₅₀ of a NoV GII.4/2006b variant at post-inoculation day (PID) 28 and monitored for 7 days post-challenge. Intestinal and systemic T cell responses were determined pre- and postchallenge. Simvastatin abolished the P particle’s protection and significantly increased diarrhea severity after NoV infection. Simvastatin decreased proliferation of virus-specific and non-specific CD8 T cells in duodenum and virus-specific CD4 and CD8 T cells in spleen and significantly reduced numbers of intestinal mononuclear cells in vaccinated pigs. Furthermore, simvastatin significantly decreased numbers of duodenal CD4+IFN-γ+, CD8+IFN-γ+ and regulatory T cells and total duodenal activated CD4+ and CD8+ T cells in vaccinated pigs pre-challenge at PID 28. Following challenge, simvastatin prevented the IFN-γ+ T cell response in spleen of vaccinated pigs. These results indicate that simvastatin abolished P particle vaccine-induced partial protection through, at least in part, impairing T cell immunity. The findings have specific implications for the development of preventive and therapeutic strategies against NoV gastroenteritis, especially for the elderly population who takes statin-type drugs.

A Norovirus Uses Bile Salts To Escape Antibody Recognition While Enhancing Receptor Binding

Noroviruses, members of the Caliciviridae family, are the major cause of epidemic gastroenteritis in humans, causing ∼20 million cases annually. These plus-strand RNA viruses have T=3 icosahedral protein capsids with 90 pronounced protruding (P) domain dimers to which antibodies and cellular receptors bind. In the case of mouse norovirus (MNV), bile salts have been shown to enhance receptor (CD300lf) binding to the P domain. We demonstrated previously that the P domains of several genotypes are markedly flexible and "float" over the shell, but the role of this flexibility was unclear. Recently, we demonstrated that bile causes a 90° rotation and collapse of the P domain onto the shell surface. Since bile binds distally to the P-shell interface, it was not at all clear how it could cause such dramatic changes. Here, we present the near-atomic resolution cryo-electron microscopy (cryo-EM) structure of the MNV protruding domain complexed with a neutralizing Fab. On the basis of previous results, we show here that bile salts cause allosteric conformational changes in the P domain that block antibody recognition of the top of the P domain. In addition, bile causes a major rearrangement of the P domain dimers that is likely responsible for the bile-induced collapse of the P domain onto the shell. In the contracted shell conformation, antibodies to the P1 and shell domains are not expected to bind. Therefore, at the site of infection in the gut, the host's own bile allows the virus to escape antibody-mediated neutralization while enhancing cell attachment. IMPORTANCE The major feature of calicivirus capsids is the 90 protruding domains (P domains) that are the site of cell receptor attachment and antibody epitopes. We demonstrated previously that these P domains are highly mobile and that bile causes these "floating" P domains in mouse norovirus (MNV) to contract onto the shell surface. Here, we present the near-atomic cryo-EM structure of the isolated MNV P domain complexed with a neutralizing Fab fragment. Our data show that bile causes two sets of changes. First, bile causes allosteric conformational changes in the epitopes at the top of the P domain that block antibody binding. Second, bile causes the P domain dimer subunits to rotate relative to each other, causing a contraction of the P domain that buries epitopes at the base of the P and shell domains. Taken together, the results show that MNV uses the host's own metabolites to enhance cell receptor binding while simultaneously blocking antibody recognition.

Antiviral Effects of Pomegranate Peel Extracts on Human Norovirus in Food Models and Simulated Gastrointestinal Fluids

Human noroviruses (HuNoV) are the dominant cause of viral gastroenteritis in all age groups worldwide. In this study, we investigated the effects of pomegranate peel extract (PPE) on the reduction of HuNoV in different food models, on surfaces of fresh produce (green onion and cherry tomato), in low-fat milk, and simulated gastrointestinal fluids. The antiviral efficacy of PPE against HuNoV was evaluated by quantifying the number of residual virus genomes using a quantitative reverse transcription PCR (qRT-PCR) assay. Pomegranate peel, considered as a waste product of industrial processing, is known for beneficial health effects and broad antimicrobial activity due to the high content of phenolic compounds and tannins. PPE showed significant antiviral properties against HuNoV both in phosphate-buffered saline (PBS) and simulated gastric fluid. The reduction of HuNoV by pomegranate juice was lower than with PPE, which could be attributed to the lower content of antimicrobial compounds. A pretreatment of cherry tomato and green onion surfaces with PPE significantly reduced the amount of HuNoV particles that adhered to those surfaces during subsequent virus suspension treatment. A detrimental effect of PPE on HuNoV structure was confirmed by transmission electron microscopy. Our results indicate that PPE is a natural antiviral agent effective against food-borne noroviruses.

Prevalence of emerging torque teno virus (TTV) in drinking water, natural waters and wastewater networks (DWNWWS): A systematic review and meta-analysis of the viral pollution marker of faecal and anthropocentric contaminations

The emerging torque teno virus (TTV) has been identified as a biohazard marker of anthropocentric pollution and contamination in drinking water, natural water and wastewater systems (DWNWWS). Therefore, this study aimed at assessing prevalence of TTV in DWNWWS. The study systematically identified and meta-analyzed published studies on TTV prevalence in DWNWWS hosted in Dimensions, Google Scholar, PubMed, Web of Science, and Scopus databases using a random-effects model and mixed-effects meta-regression model for sensitivity analysis. Furthermore, the meta-analysis was stratified to estimate water type-specific TTV prevalence. The study found a total of 58 articles, of which 13 articles subdivided into 31 studies with 374 TTV positive cases and 862 total sample sizes were systematically reviewed and meta-analyzed. The pooled prevalence of TTV in DWNWWS was 37.18% (95%CI: 23.76-55.55%). Prevalence of TTV was significantly different across water types and it was 56.67% (95%CI: 36.94-75.46%) in wastewater, 26.72% (95%CI: 6.87-52.56%) in river water, and 17.17% (95%CI: 0.54-45.39%) in drinking water. TTV incidence in seawater and groundwater was 0% and 25.0% respectively. Funnel plots constructed and associated statistics of rank correlation test and Egger's regression test in this study, show lack of publication bias in the pooled prevalence of TTV in DWNWWS. Although, sample type (QM(df = 1) = 6.9656, p = 0.0083) and concentration methods (QM(df = 1) = 3.8055, p = 0.0511) significantly moderated and accounted for 15.39% and 6.00% of heterogeneity in the prevalence of TTV in DWNWWS respectively. In conclusion, research focus/monitoring activities on TTV is generally inadequate and potential risk of TTV in DWNWWS is underappreciated in most nations; the analyzed studies were from 7 countries (USA, Japan, Italy, Iran, Germany, Egypt, and Brazil). Finally, inefficient concentration method severely influences the prevalence of TTV in DWNWWS and could give rise to underestimation of TTV and mar TTV-based source-tracking of anthropogenic pollutions.

Cost-effectiveness of pediatric norovirus vaccination in daycare settings

Objective:

Noroviruses are the leading cause of acute gastroenteritis in the United States and outbreaks frequently occur in daycare settings. Results of norovirus vaccine trials have been promising, however there are open questions as to whether vaccination of daycare children would be cost-effective. We investigated the incremental cost-effectiveness of a hypothetical norovirus vaccination for children in daycare settings compared to no vaccination.

Methods:

We conducted a model-based cost-effectiveness analysis using a disease transmission model of children attending daycare. Vaccination with a 90% coverage rate in addition to the observed standard of care (exclusion of symptomatic children from daycare) was compared to the observed standard of care. The main outcomes measures were infections and deaths averted, quality-adjusted life years (QALYs), costs, and incremental cost-effectiveness ratio (ICER). Cost-effectiveness was analyzed from a societal perspective, including medical costs to children as well as productivity losses of parents, over a two-year time horizon. Data sources included outbreak surveillance data and published literature.

Results:

A 50% efficacious norovirus vaccine averts 571.83 norovirus cases and 0.003 norovirus-related deaths per 10,000 children compared to the observed standard of care. A $200 norovirus vaccine that is 50% efficacious has a net cost increase of $178.10 per child and 0.025 more QALYs, resulting in an ICER of $7,028/QALY. Based on the probabilistic sensitivity analysis, we estimated that a $200 vaccination with 50% efficacy was 94.0% likely to be cost-effective at a willingness-to-pay of $100,000/QALY threshold and 95.3% likely at a $150,000/QALY threshold.

Conclusion:

Due to the large disease burden associated with norovirus, it is likely that vaccinating children in daycares could be cost-effective, even with modest vaccine efficacy and a high per-child cost of vaccination. Norovirus vaccination of children in daycare has a cost-effectiveness ratio similar to other commonly recommended childhood vaccines.

Potential Clinical and Economic Value of Norovirus Vaccination in the Community Setting

INTRODUCTION

With norovirus vaccine candidates currently under development, now is the time to identify the vaccine characteristics and implementation thresholds at which vaccination becomes cost effective and cost saving in a community setting.

METHODS

In 2020, a norovirus transmission, clinical, and economics computational simulation model representing different U.S. population segments was developed to simulate the spread of norovirus and the potential impact of vaccinating children aged <5 years and older adults (aged ≥65 years).

RESULTS

Compared with no vaccination, vaccinating preschool-aged children averted 8%-72% of symptomatic norovirus cases in a community, whereas vaccinating older adults averted 2%-29% of symptomatic cases (varying with vaccine efficacy [25%-75%] and vaccination coverage [10%-80%]). Vaccination with a 25% vaccine efficacy was cost effective (incremental cost-effectiveness ratio ≤$50,000 per quality-adjusted life year) when vaccination cost ≤$445 and cost saving at ≤$370 when vaccinating preschool-aged children and ≤$42 and ≤$30, respectively, when vaccinating older adults. With a 50% vaccine efficacy, vaccination was cost effective when it cost ≤$1,190 and cost saving at ≤$930 when vaccinating preschool-aged children and ≤$110 and ≤$64, respectively, when vaccinating older adults. These cost thresholds (cost effective and cost saving, respectively) further increased with a 75% vaccine efficacy to ≤$1,600 and ≤$1,300 for preschool-aged children and ≤$165 and ≤$100 for older adults.

CONCLUSIONS

This study outlines thresholds at which a norovirus vaccine would be cost effective and cost saving in the community when vaccinating children aged <5 years and older adults. Establishing these thresholds can help provide decision makers with targets to consider when developing and implementing a norovirus vaccine.