Effects of face masks and ventilation on the risk of SARS-CoV-2 respiratory transmission in public toilets: a quantitative microbial risk assessment

Applications of Quantitative Microbial Risk Assessment to Respiratory Pathogens and Implications for Uptake in Policy: A State-of-the-Science Review

BACKGROUND

Respiratory tract infections are major contributors to the global disease burden. Quantitative microbial risk assessment (QMRA) holds potential as a rapidly deployable framework to understand respiratory pathogen transmission and inform policy on infection control.

OBJECTIVES

The goal of this paper was to evaluate, motivate, and inform further development of the use of QMRA as a rapid tool to understand the transmission of respiratory pathogens and improve the evidence base for infection control policies.

METHODS

We conducted a literature review to identify peer-reviewed studies of complete QMRA frameworks on aerosol inhalation or contact transmission of respiratory pathogens. From each of the identified studies, we extracted and summarized information on the applied exposure model approaches, dose-response models, and parameter values, including risk characterization. Finally, we reviewed linkages between model outcomes and policy.

RESULTS

We identified 93 studies conducted in 16 different countries with complete QMRA frameworks for diverse respiratory pathogens, including SARS-CoV-2, Legionella spp., Staphylococcus aureus, influenza, and Bacillus anthracis. Six distinct exposure models were identified across diverse and complex transmission pathways. In 57 studies, exposure model frameworks were informed by their ability to model the efficacy of potential interventions. Among interventions, masking, ventilation, social distancing, and other environmental source controls were commonly assessed. Pathogen concentration, aerosol concentration, and partitioning coefficient were influential exposure parameters as identified by sensitivity analysis. Most (84%, n = 78 ) studies presented policy-relevant content including a) determining disease burden to call for policy intervention, b) determining risk-based threshold values for regulations, c) informing intervention and control strategies, and d) making recommendations and suggestions for QMRA application in policy.

CONCLUSIONS

We identified needs to further the development of QMRA frameworks for respiratory pathogens that prioritize appropriate aerosol exposure modeling approaches, consider trade-offs between model validity and complexity, and incorporate research that strengthens confidence in QMRA results. https://doi.org/10.1289/EHP12695.

Quantitative microbial risk assessment of the gastrointestinal risks to swimmers at Southeast Asian urban beaches using site-specific and combined autochthonous and fecal bacteria exposure data

Recreational exposure to microbial pollution at urban beaches poses a health risk to beachgoers. The accurate quantification of such risks is crucial in managing beaches effectively and establishing warning guidelines. In this study, we employed a quantitative microbial risk assessment (QMRA) framework to assess marine water quality and estimate the risks associated with Vibrio parahaemolyticus, an autochthonous pathogen that causes gastrointestinal illnesses, and enterococci, a traditional fecal bacteria indicator. The microbial contamination levels of V. parahaemolyticus and enterococci were determined from 48 water samples collected at two beaches in Thailand during dry and wet seasons. The accidentally ingested water volumes were obtained through a survey involving 438 respondents. The probability of illness (Pill) was estimated using dose-response models and Monte Carlo simulation. The results revealed that enterococci posed a higher risk of illness than V. parahaemolyticus at all seven study sites. The median combined gastrointestinal (GI) risk from both bacteria at all sites met the US EPA risk benchmark of 0.036 and the 0.05 benchmark set by the WHO, but the 95th percentile risk data at all sites exceeded the benchmarks. This emphasizes the need for the continuous monitoring and management of microbial pollution at these sites. The site-specific exposure data showed higher estimated risks with increased variations compared to the WHO-referenced values, which highlights the significance of locally measured microbial concentrations and survey exposure data to avoid underestimation. Estimating the risks from recreational exposure to waterborne bacteria can inform beach management policies aimed at reducing public health risks to swimmers. The study findings improve the understanding of the risks associated with water recreation activities at Southeast Asian beaches and offer valuable insights for the development of water quality guidelines, which are crucial for the sustainable development of the blue economy.

Evaluating the threshold limit value of acceptable exposure concentration for exposure to bioaerosols in a wastewater treatment plant: Reverse-quantitative microbial risk assessment and sensitivity analysis

Agitation operations produce numerous pathogenic bioaerosols in WWTPs¹. QMRA² can determine risks of persons exposed to these bioaerosols. However, QMRA framework cannot help stakeholders in immediately deciding whether a risk is intolerable. Thus, evaluating threshold of acceptable exposure concentration is an urgent issue but is still rarely addressed in WWTPs. This study analyzed TLV³ benchmarks of E. coli and S. aureus bioaerosols emitted from a WWTP by reverse-QMRA. Furthermore, variance of input parameters was clarified by sensitivity analysis. Results showed that, under conservative and optimistic estimates, TLV of technicians was 1.52-2.06 and 1.26-1.68 times as large as those of workers, respectively; wearing mask drive TLV up to 1-2 orders of magnitude; TLV of M⁴ was at most 1.33 and 1.31 times as large as that of RD⁵, respectively. For sensitivity analysis, removal fraction by equipping PPE enlarge TLV for effortlessly obtaining an acceptable assessment result; exposure time was dominant when without PPE excepting the scenario of technicians exposed to E. coli bioaerosol. This study helps establish threshold guidelines for bioaerosols in WWTPs and contribute innovative perspectives for stakeholders.

Comparative genomic analyses of pathogenic bacteria and viruses and antimicrobial resistance genes in an urban transportation canal

Water commuting is a major urban transportation method in Thailand. However, urban boat commuters risk exposure to microbially contaminated bioaerosols or splash. We aimed to investigate the microbial community structures, identify bacterial and viral pathogens, and assess the abundance of antimicrobial resistance genes (ARGs) using next-generation sequencing (NGS) at 10 sampling sites along an 18 km transportation boat route in the Saen Saep Canal, which traverses cultural, commercial, and suburban land-based zones. The shotgun metagenomic (Illumina HiSeq) and 16S rRNA gene amplicon (V4 region) (Illumina MiSeq) sequencing platforms revealed diverse microbial clusters aligned with the zones, with explicit segregation between the cultural and suburban sites. The shotgun metagenomic sequencing further identified bacterial and viral pathogens, and ARGs. The predominant bacterial pathogens (>0.5 % relative abundance) were the Burkholderia cepacia complex, Arcobacter butzleri, Burkholderia vietnamiensis, Klebsiella pneumoniae, and the Enterobacter cloacae complex. The viruses (0.28 %-0.67 % abundance in all microbial sequences) comprised mainly vertebrate viruses and bacteriophages, with encephalomyocarditis virus (33.3 %-58.2 % abundance in viral sequences), hepatitis C virus genotype 1, human alphaherpesvirus 1, and human betaherpesvirus 6A among the human viral pathogens. The 15 ARG types contained 611 ARG subtypes, including those resistant to beta-lactam, which was the most diverse and abundant group (206 subtypes; 17.0 %-27.5 %), aminoglycoside (94 subtypes; 9.6 %-15.3 %), tetracycline (80 subtypes; 15.6 %-20.2 %), and macrolide (79 subtypes; 14.5 %-32.1 %). Interestingly, the abundance of ARGs associated with resistance to beta-lactam, trimethoprim, and sulphonamide, as well as A. butzleri and crAssphage, at the cultural sites was significantly different from the other sites (p < 0.05). We demonstrated the benefits of using NGS to deliver insights into microbial communities, and antimicrobial resistance, both of which pose a risk to human health. Using NGS may facilitate microbial risk mitigation and management for urban water commuters and proximal residents.

Developing occupational and health susceptibility personas for wastewater personnel in the United States in the age of COVID-19

Compared with the public, wastewater personnel, are at an increased risk of infection and illness from wastewater pathogens due to work-related tasks. Unfortunately, current risk assessment approaches do not consider individual personnel factors (e.g., age and health conditions) that may influence their susceptibility to a health effect. The objective of this study is to establish a baseline level of occupational and health factors among the wastewater personnel population, quantify these factors using a susceptibility evaluation scoring system, and examine relevant susceptibility features using the concept of "Personas." Using survey data from 246 respondents and public health risk data on COVID-19 from the CDC, personnel clustered into three persona groups: "low susceptibility," "high occupational susceptibility," and "high health susceptibility." Results highlight the intersectionality between gender, age, underlying health conditions, job tasks, and level of exposure to wastewater and provide context for incorporating individual variables into risk assessment methodologies with the goal of protecting this essential workforce. PRACTITIONER POINTS: A risk assessment framework that combines health and occupational susceptibility factors was developed for wastewater treatment plant personnel. Wastewater personnel clustered into three persona groups: "low susceptibility," "high occupational susceptibility," and "high health susceptibility." The intersectionality between job related activities and individual health provides a holistic approach to risk assessment for wastewater personnel.