Aerosol-Transmitted Infections-a New Consideration for Public Health and Infection Control Teams

Symptom propagation in respiratory pathogens of public health concern: a review of the evidence

Symptom propagation occurs when the symptom set an individual experiences is correlated with the symptom set of the individual who infected them. Symptom propagation may dramatically affect epidemiological outcomes, potentially causing clusters of severe disease. Conversely, it could result in chains of mild infection, generating widespread immunity with minimal cost to public health. Despite accumulating evidence that symptom propagation occurs for many respiratory pathogens, the underlying mechanisms are not well understood. Here, we conducted a scoping literature review for 14 respiratory pathogens to ascertain the extent of evidence for symptom propagation by two mechanisms: dose-severity relationships and route-severity relationships. We identify considerable heterogeneity between pathogens in the relative importance of the two mechanisms, highlighting the importance of pathogen-specific investigations. For almost all pathogens, including influenza and SARS-CoV-2, we found support for at least one of the two mechanisms. For some pathogens, including influenza, we found convincing evidence that both mechanisms contribute to symptom propagation. Furthermore, infectious disease models traditionally do not include symptom propagation. We summarize the present state of modelling advancements to address the methodological gap. We then investigate a simplified disease outbreak scenario, finding that under strong symptom propagation, isolating mildly infected individuals can have negative epidemiological implications.

Air Change Rate and SARS-CoV-2 Exposure in Hospitals and Residences: A Meta-Analysis

As SARS-CoV-2 swept across the globe, increased ventilation and implementation of air cleaning were emphasized by the US CDC and WHO as important strategies to reduce the risk of inhalation exposure to the virus. To assess whether higher ventilation and air cleaning rates lead to lower exposure risk to SARS-CoV-2, 1274 manuscripts published between April 2020 and September 2022 were screened using key words "airborne SARS-CoV-2 or "SARS-CoV-2 aerosol". Ninety-three studies involved air sampling at locations with known sources (hospitals and residences) were selected and associated data were compiled. Two metrics were used to assess exposure risk: SARS-CoV-2 concentration and SARS-CoV-2 detection rate in air samples. Locations were categorized by type (hospital or residence) and proximity to the sampling location housing the isolated/quarantined patient (primary or secondary). The results showed that hospital wards had lower airborne virus concentrations than residential isolation rooms. A negative correlation was found between airborne virus concentrations in primary-occupancy areas and air changes per hour (ACH). In hospital settings, sample positivity rates were significantly reduced in secondary-occupancy areas compared to primary-occupancy areas, but they were similar across sampling locations in residential settings. ACH and sample positivity rates were negatively correlated, though the effect was diminished when ACH values exceeded 8. While limitations associated with diverse sampling protocols exist, data considered by this meta-analysis support the notion that higher ACH may reduce exposure risks to the virus in ambient air.

Antimicrobial activity of silver-copper coating against aerosols containing surrogate respiratory viruses and bacteria

The transmission of bacteria and respiratory viruses through expelled saliva microdroplets and aerosols is a significant concern for healthcare workers, further highlighted during the SARS-CoV-2 pandemic. To address this issue, the development of nanomaterials with antimicrobial properties for use as nanolayers in respiratory protection equipment, such as facemasks or respirators, has emerged as a potential solution. In this study, a silver and copper nanolayer called SakCu® was deposited on one side of a spun-bond polypropylene fabric using the magnetron sputtering technique. The antibacterial and antiviral activity of the AgCu nanolayer was evaluated against droplets falling on the material and aerosols passing through it. The effectiveness of the nanolayer was assessed by measuring viral loads of the enveloped virus SARS-CoV-2 and viability assays using respiratory surrogate viruses, including PaMx54, PaMx60, PaMx61 (ssRNA, Leviviridae), and PhiX174 (ssDNA, Microviridae) as representatives of non-enveloped viruses. Colony forming unit (CFU) determination was employed to evaluate the survival of aerobic and anaerobic bacteria. The results demonstrated a nearly exponential reduction in SARS-CoV-2 viral load, achieving complete viral load reduction after 24 hours of contact incubation with the AgCu nanolayer. Viability assays with the surrogate viruses showed a significant reduction in viral replication between 2-4 hours after contact. The simulated viral filtration system demonstrated inhibition of viral replication ranging from 39% to 64%. The viability assays with PhiX174 exhibited a 2-log reduction in viral replication after 24 hours of contact and a 16.31% inhibition in viral filtration assays. Bacterial growth inhibition varied depending on the species, with reductions ranging from 70% to 92% for aerobic bacteria and over 90% for anaerobic strains. In conclusion, the AgCu nanolayer displayed high bactericidal and antiviral activity in contact and aerosol conditions. Therefore, it holds the potential for incorporation into personal protective equipment to effectively reduce and prevent the transmission of aerosol-borne pathogenic bacteria and respiratory viruses.

NS, Víšová I, Vrabcová M, Houska M, Anthi J, Spasovová M, Mustacová J, Štěrba J, Dostálek J, Tung CP, Yang AS, Jack R, Dejneka A, Hajdu J, Vaisocherová-Lísalová H. Negligible risk of surface transmission of SARS-CoV-2 in public transportation

BACKGROUND

Exposure to pathogens in public transport systems is a common means of spreading infection, mainly by inhaling aerosol or droplets from infected individuals. Such particles also contaminate surfaces, creating a potential surface-transmission pathway.

METHODS

A fast acoustic biosensor with an antifouling nano-coating was introduced to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on exposed surfaces in the Prague Public Transport System. Samples were measured directly without pre-treatment. Results with the sensor gave excellent agreement with parallel quantitative reverse-transcription polymerase chain reaction (qRT-PCR) measurements on 482 surface samples taken from actively used trams, buses, metro trains and platforms between 7 and 9 April 2021, in the middle of the lineage Alpha SARS-CoV-2 epidemic wave when 1 in 240 people were COVID-19 positive in Prague.

RESULTS

Only ten of the 482 surface swabs produced positive results and none of them contained virus particles capable of replication, indicating that positive samples contained inactive virus particles and/or fragments. Measurements of the rate of decay of SARS-CoV-2 on frequently touched surface materials showed that the virus did not remain viable longer than 1-4 h. The rate of inactivation was the fastest on rubber handrails in metro escalators and the slowest on hard-plastic seats, window glasses and stainless-steel grab rails. As a result of this study, Prague Public Transport Systems revised their cleaning protocols and the lengths of parking times during the pandemic.

CONCLUSIONS

Our findings suggest that surface transmission played no or negligible role in spreading SARS-CoV-2 in Prague. The results also demonstrate the potential of the new biosensor to serve as a complementary screening tool in epidemic monitoring and prognosis.

Assessment of the aetiology of acute gastroenteritis outbreaks in infants reveals rotavirus, noroviruses and adenovirus prevalence and viral coinfections in Nsukka, Nigeria

A better understanding of the aetiology of acute gastroenteritis (AGE) outbreaks in Southeast Nigeria would help safeguarding public health. This study screened stool samples collected from infants (children < 5 years of age) attending selected hospitals in Nsukka for human enteric viruses and evaluated the seasonality of AGE based on three-year records available at selected hospitals. A total of 120 stool samples (109 from diarrhoeal-patients and 11 from non-diarrhoeal patients, as control) collected during the AGE outbreaks of January - March 2019 and January-February 2020. The samples were analysed using an immunochromatographic lateral flow assay for differential qualitative detection of rotavirus (RoV), adenovirus (AdV), and norovirus genogroups I and II (NoVI, NoVII). Three-year (2017-2019) retrospective data on the cases of AGE reported at the hospitals were also collected and analysed. The overall prevalence of acute gastroenteritis was high (75.83%), with 13.19%representing viral co-infections. Rotavirus detection rate (69.17%) was higher than that for other viral agents (15.83%). Both mono- and mixed infections were observed for RoV, AdV and NoVII, whereas NoVI was detected only in co-infection cases. Analysis of risk factors showed that acute gastroenteritis was detected more often in infants of age ˂1 year (73.53%) than in those 1 ≤ 2 years (22.55%) or > 2 years (3.92%) in age. Gender and age were not associated with the cases of co-infections (p˂0.05). The seasonality data indicated one peak of the infection occurring in January 2017 which has decreased consecutively in the subsequent two years. These results demonstrate the prevalence and co-occurrence of enteric viruses in cases of infantile diarrhoea in Nsukka. Further molecular characterization of enteric virus strains, especially noroviruses, in this region would contribute significantly to global epidemiological data.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-023-00821-2.

Far-UVC (222 nm) efficiently inactivates an airborne pathogen in a room-sized chamber

Many infectious diseases, including COVID-19, are transmitted by airborne pathogens. There is a need for effective environmental control measures which, ideally, are not reliant on human behaviour. One potential solution is Krypton Chloride (KrCl) excimer lamps (often referred to as Far-UVC), which can efficiently inactivate pathogens, such as coronaviruses and influenza, in air. Research demonstrates that when KrCl lamps are filtered to remove longer-wavelength ultraviolet emissions they do not induce acute reactions in the skin or eyes, nor delayed effects such as skin cancer. While there is laboratory evidence for Far-UVC efficacy, there is limited evidence in full-sized rooms. For the first time, we show that Far-UVC deployed in a room-sized chamber effectively inactivates aerosolised Staphylococcus aureus. At a room ventilation rate of 3 air-changes-per-hour (ACH), with 5 filtered-sources the steady-state pathogen load was reduced by 98.4% providing an additional 184 equivalent air changes (eACH). This reduction was achieved using Far-UVC irradiances consistent with current American Conference of Governmental Industrial Hygienists threshold limit values for skin for a continuous 8-h exposure. Our data indicate that Far-UVC is likely to be more effective against common airborne viruses, including SARS-CoV-2, than bacteria and should thus be an effective and "hands-off" technology to reduce airborne disease transmission. The findings provide room-scale data to support the design and development of effective Far-UVC systems.

Ability of Essential Oil Vapours to Reduce Numbers of Culturable Aerosolised Coronavirus, Bacteria and Fungi

Transmission of pathogens present in the indoor air can occur through aerosols. This study evaluated the efficacy of an evaporated mix of essential oils to reduce the numbers of culturable aerosolized coronavirus, bacterium and fungus. The essential oil-containing gel was allowed to vaporize inside a glass chamber for 10 or 20 min. Aerosols of a surrogate of SARS-CoV-2, murine hepatitis coronavirus MHV-1, Escherichia coli or Aspergillus flavus spores were produced using a collision nebuliser and passed through the essential oil vapours, then collected on a six-stage Andersen sampler. The six-stages of the impact sampler capture aerosols in sizes ranging from 7 to 0.65 µm. The number of culturable microbes present in the aerosols collected in the different stages were enumerated and compared to the number of culturable microbes in control microbial aerosols that were not exposed to the evaporated essential oils. After 10 and 20 min evaporation, the essential oils reduced the numbers of culturable aerosolized coronavirus by 48% (log₁₀ reduction = 0.3; p = 0.002 vs. control) and 53% (log₁₀ reduction = 0.3; p = 0.001 vs. control), respectively. The essential oils vaporised for 10 min, reduced the number of viable E. coli by 51% (log₁₀ reduction = 0.3; p = 0.032 vs. control). The Aspergillus flavus spores were mostly observed in the larger aerosols (7.00 µm to 2.10 µm) and the essential oils vaporised for 10 min reduced the number of viable spores by 72% (log₁₀ reduction = 0.6; p = 0.008 vs. control). The vapours produced by a gel containing naturally occurring essential oils were able to significantly reduce the viable numbers of aerosolized coronavirus, bacteria and fungal spores. The antimicrobial gel containing the essential oils may be able to reduce aerosol transmission of microbes when used in domestic and workplace settings.

Fungi in the indoor air of critical hospital areas: a review

Invasive fungal infection is an important cause of mortality and morbidity in neonates, especially in low-birthweight neonates. The contribution of fungi in the indoor air to the incidence of mucocutaneous colonization and to the risk of invasive fungal infection in this population is uncertain. This review aimed to identify and to summarize the best available evidence on the fungal contamination in the indoor air of critical hospital areas with an emphasis on pediatric/neonatal ICUs. Publications from 2005 to 2019 were searched in the databases Scientific Electronic Library Online (SciELO), US National Library of Medicine National Institutes of Health Search (PubMed), and Latin American Caribbean Health Sciences (LILACS). Descriptors in Health Sciences (DeCS) were used. Research papers published in Portuguese, English, and Spanish were included. Twenty-nine papers on all continents except Australia were selected. The results showed that the air mycobiota contained several fungal species, notably Aspergillus, Penicillium, Cladosporium, Fusarium, and yeast (Candida) species. The selected papers point out the risks that fungi pose to neonates, who have immature immune system, and describe simultaneous external factors (air humidity, seasonality, air and people flow, use of particulate filters, and health professionals' hand hygiene) that contribute to indoor air contamination with fungi. Improving communication among health professionals is a great concern because this can prevent major health complications in neonates, especially in low-birthweight neonates. The results reinforced the need to monitor environmental fungi more frequently and efficiently in hospitals, especially in neonatal ICUs.

Simplicial SIRS epidemic models with nonlinear incidence rates

Mathematical epidemiology that describes the complex dynamics on social networks has become increasingly popular. However, a few methods have tackled the problem of coupling network topology with complex incidence mechanisms. Here, we propose a simplicial susceptible-infected-recovered-susceptible (SIRS) model to investigate the epidemic spreading via combining the network higher-order structure with a nonlinear incidence rate. A network-based social system is reshaped to a simplicial complex, in which the spreading or infection occurs with nonlinear reinforcement characterized by the simplex dimensions. Compared with the previous simplicial susceptible-infected-susceptible (SIS) models, the proposed SIRS model can not only capture the discontinuous transition and the bistability of a complex system but also capture the periodic phenomenon of epidemic outbreaks. More significantly, the two thresholds associated with the bistable region and the critical value of the reinforcement factor are derived. We further analyze the stability of equilibrium points of the proposed model and obtain the condition of existence of the bistable states and limit cycles. This work expands the simplicial SIS models to SIRS models and sheds light on a novel perspective of combining the higher-order structure of complex systems with nonlinear incidence rates.

Experimental Evaluation of Aerosol Production after Dental Ultrasonic Instrumentation: An Analysis on Fine Particulate Matter Perturbation

Aerosol production represents a major concern during the majority of dental procedures. The aim of the present study is to investigate the dynamics of aerosol particles after 15 min of continuous supragingival ultrasonic instrumentation with no attempt of containment through particle count analysis. Eight volunteers were treated with supragingival ultrasonic instrumentation of the anterior buccal region. A gravimetric impactor was positioned 1 m away and at the same height of the head of the patient. Particles of different sizes (0.3–10 µm) were measured at the beginning of instrumentation, at the end of instrumentation (EI), and then every 15 min up to 105 min. The 0.3-µm particles showed non-significant increases at 15/30 min. The 0.5–1-µm particles increased at EI (p < 0.05), and 0.5 µm remained high for another 15 min. Overall, all submicron aerosol particles showed a slow decrease to normal values. Particles measuring 3–5 µm showed non-significant increases at EI. Particles measuring 10 µm did not show any increases but a continuous reduction (p < 0.001 versus 0.3 µm, p < 0.01 versus 0.5 µm, and p < 0.05 versus 1–3 µm). Aerosol particles behaved differently according to their dimensions. Submicron aerosols peaked after instrumentation and slowly decreased after the end of instrumentation, whilst larger particles did not show any significant increases. This experimental study produces a benchmark for the measurement of aerosol particles during dental procedures and raises some relevant concerns about indoor air quality after instrumentation.

Multi-Scale Airborne Infectious Disease Transmission

Airborne disease transmission is central to many scientific disciplines including agriculture, veterinary biosafety, medicine, and public health. Legal and regulatory standards are in place to prevent agricultural, nosocomial, and community airborne disease transmission. However, the overall importance of the airborne pathway is underappreciated, e.g.,, US National Library of Medicine's Medical Subjects Headings (MESH) thesaurus lacks an airborne disease transmission indexing term. This has practical consequences as airborne precautions to control epidemic disease spread may not be taken when airborne transmission is important, but unrecognized. Publishing clearer practical methodological guidelines for surveillance studies and disease outbreak evaluations could help address this situation.To inform future work, this paper highlights selected, well-established airborne transmission events - largely cases replicated in multiple, independently conducted scientific studies. Methodologies include field experiments, modeling, epidemiology studies, disease outbreak investigations and mitigation studies. Collectively, this literature demonstrates that airborne viruses, bacteria, and fungal pathogens have the capability to cause disease in plants, animals, and humans over multiple distances - from near range (< 5 m) to continental (> 500 km) in scale. The plausibility and implications of undetected airborne disease transmission are discussed, including the notable underreporting of disease burden for several airborne transmitted diseases.

Are Smoke and Aerosols Generated During Laparoscopic Surgery a Biohazard? A Systematic Evidence-Based Review

Background. Laparoscopic surgery generates end products that can have potentially harmful effects for the surgical team from short- or long-time exposure. In view of the current SARS-CoV-2 circumstances, controversy has risen concerning the safety of surgical smoke (SS) and aerosols and the perception of an increased risk of exposure during laparoscopic surgery. Methods. The present qualitative systematic review was conducted according to Meta-Analyses and Systematic Reviews of Observational Studies (MOOSE). A literature search was performed from March 2020 up to May 10, 2020, using the PubMed database, Cochrane, and Google Scholar to assess the risk of airborne transmission of viruses and the potential health risk of surgical smoke- and aerosol-generating procedures produced during laparoscopic surgery. The keywords were introduced in combination to obtain better search results. Application of the inclusion and exclusion criteria identified 44 relevant articles. Results. Genetic material from certain viruses, or the virus itself, has been detected in SS and aerosols. However, in the current SARS-CoV-2, as in other coronavirus situations, studies analyzing the presence of airborne transmission of viruses in surgical smoke are lacking. Conclusion. Despite the lack of clear evidence regarding the risk of diseases as the result of smoke- and aerosol-generating procedures during laparoscopic surgery, further investigation is needed. Meanwhile, all available precautions must be taken.

Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)

The coronavirus disease 2019 (COVID-19) pandemic has caused untold disruption throughout the world. Understanding the mechanisms for transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is key to preventing further spread, but there is confusion over the meaning of ‘airborne’ whenever transmission is discussed. Scientific ambivalence originates from evidence published many years ago which has generated mythological beliefs that obscure current thinking. This article collates and explores some of the most commonly held dogmas on airborne transmission in order to stimulate revision of the science in the light of current evidence. Six ‘myths’ are presented, explained and ultimately refuted on the basis of recently published papers and expert opinion from previous work related to similar viruses. There is little doubt that SARS-CoV-2 is transmitted via a range of airborne particle sizes subject to all the usual ventilation parameters and human behaviour. Experts from specialties encompassing aerosol studies, ventilation, engineering, physics, virology and clinical medicine have joined together to produce this review to consolidate the evidence for airborne transmission mechanisms, and offer justification for modern strategies for prevention and control of COVID-19 in health care and the community.

Arguments pour une possible transmission par voie aérienne du SARS-CoV-2 dans la crise COVID-19

La connaissance des modes de transmission du SARS-CoV-2 est un élément fondamental dans l’élaboration des stratégies de prévention en santé au travail et en santé publique dans le cadre de la gestion de crise du Covid-19. Le SARS-CoV-2 est retrouvé dans les voies aériennes des patients, y compris asymptomatiques. Les données récentes de la littérature suggèrent un risque de transmission du SARS-CoV-2 par voie aérienne qui a probablement été sous-estimé, notamment via des aérosols générés par la toux ou les éternuements, mais aussi plus simplement la parole et la respiration, et donc la composition est majoritairement le fait de particules dont le diamètre est inférieur ou égal à 1 μm. Des données préliminaires montrent la présence d’ARN viral dans l’air et sur des surfaces distantes des patients sources. Cependant, il est important de noter que la détection de matériel génétique viral par RT-PCR ne signifie pas que le virus soit vivant et infectant. En fonction de données sur la quantification du pouvoir infectant des aérosols de petite taille et si l’hypothèse d’une telle transmission était confirmée, les indications de port des protections respiratoires de type FFP2 mériteraient d’être élargies, notamment en milieu de soin.

A numerical study of ventilation strategies for infection risk mitigation in general inpatient wards

Aerial dispersion of human exhaled microbial contaminants and subsequent contamination of surfaces is a potential route for infection transmission in hospitals. Most general hospital wards have ventilation systems that drive air and thus contaminants from the patient areas towards the corridors. This study investigates the transport mechanism and deposition patterns of Middle East Respiratory Syndrome Coronavirus (MERS-CoV) within a typical six bedded general inpatient ward cubicle through numerical simulation. It demonstrates that both air change and exhaust airflow rates have significant effects on not only the airflow but also the particle distribution within a mechanically ventilated space. Moreover, the location of an infected patient within the ward cubicle is crucial in determining the extent of infection risk to other ward occupants. Hence, it is recommended to provide exhaust grilles in close proximity to a patient, preferably above each patient's bed. To achieve infection prevention and control, high exhaust airflow rate is also suggested. Regardless of the ventilation design, all patients and any surfaces within a ward cubicle should be regularly and thoroughly cleaned and disinfected to remove microbial contamination. The outcome of this study can serve as a source of reference for hospital management to better ventilation design strategies for mitigating the risk of infection.

Isolating infectious patients: organizational, clinical, and ethical issues

BACKGROUND

Isolating infectious patients is essential to reduce infection risk. Effectiveness depends on identifying infectious patients, transferring them to suitable accommodations, and maintaining precautions.

METHODS

Online study to address identification of infectious patients, transfer, and challenges of maintaining isolation in hospitals in the United Kingdom.

RESULTS

Forty-nine responses were obtained. Decision to isolate is made by infection prevention teams, clinicians, and managers. Respondents reported situations where isolation was impossible because of the patient's physical condition or cognitive status. Very sick patients and those with dementia were not thought to tolerate isolation well. Patients were informed about the need for isolation by ward nurses, sometimes with explanations from infection prevention teams. Explanations were often poorly received and comprehended, resulting in complaints. Respondents were aware of ethical dilemmas associated with isolation that is undertaken in the interests of other health service users and society. Organizational failures could delay initaiting isolation. Records were kept of the demand for isolation and/or uptake, but quality was variable.

CONCLUSION

Isolation has received the most attention in countries with under-provision of accommodations. Our study characterizes reasons for delays in identifying patients and failures of isolation, which place others at risk and which apply to any organization regardless of availability. It also highlights the ethical dilemmas of enforcing isolation.