Extension of probability models of the risk of infections by human enteric viruses

This study presents a novel approach for obtaining reliable models and coefficients to estimate the probability of infection caused by common human enteric viruses. The aim is to provide guidance for public health policies in disease prevention and control, by reducing uncertainty and management costs in health risk assessments. Conventional dose-response (DR) models, based on the theory elaborated by Furumoto and Mickey [1], exhibit limitations stemming from the heterogeneity of individual host susceptibilities to infection resulting from ingesting aggregate viruses. Moreover, the scarcity of well-designed viral challenge experiments contributes to significant uncertainty in these DR models. To address these issues, we conducted a review of infection models used in health risk analysis, focusing on Norovirus (NoV) GI.1, pooled Enterovirus group (EV), Poliovirus 1/SM, and Echo-12 virus via contaminated water or food. Using a mechanistic approach, we reevaluated the known DR models and coefficients for the probability of individual host infection in the mentioned viruses based on dose-infection challenge experiments. Specifically, we sought to establish a relationship between the minimum infectious dose (ID) and the ID having a 50% probability of initiating host infection in the same challenge experiment. Furthermore, we developed a new formula to estimate the degree of aggregation of GI.1 NoV at the mean infectious dose. The proposed models, based on "exact" beta-Poisson DR models, effectively predicted infection probabilities from ingestion of both disaggregated and aggregate NoV GI.1. Through a numerical evaluation, we compared the results with the maximum likelihood estimation (MLE) probability obtained from a controlled challenge trial with the NoV GI.1 virus described in the literature, demonstrating the accuracy of our approach. By addressing the indetermination of the unmeasured degree of NoV aggregation in each single infectious dose, our models reduce overestimations and uncertainties in microbial risk assessments. This improvement enhances the management of health risks associated with enteric virus infections.

Comparison of the risk of infection of human rotavirus and astrovirus according to fishing and swimming activities at Las Cañas beach, Uruguay

AIMS

To estimate the risk of human Rotavirus (RV) and Astrovirus (HAstV) infections for swimmers and fishers at Las Cañas beach, Uruguay.

METHODS AND RESULTS

Surface water samples were collected monthly for one year. The dose response models used were β Poisson and ₁ F₁ hypergeometric for RV and HAstV, respectively. The probabilities of infection were calculated using a kernel density estimate to fitting the data and then sampling from this distribution (Monte Carlo simulation). The probability of RV infection for fishers was between 0 and 65% and for swimmers was between 0 and 50% (<18 years old) and between 0 and 38% (>18 years old). For HAstV, the probability of infection for fishers was between 0% and 45% and for swimmers was between 0 and 38% (<18 years old) and between 0 and 18% (>18 years old).

CONCLUSIONS

This study suggests that fishers are at higher risk of infection for both viruses when compared with swimmers mainly due to higher viral frequency and concentration at the site for fishing activities.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study highlights the different risk of infection for Rotavirus and Astrovirus, determined according to two popular activities such as swimming and fishing evidencing their negative impact in public health when contaminated waters are used mainly in developing countries like Uruguay.

Statewide Quantitative Microbial Risk Assessment for Waterborne Viruses, Bacteria, and Protozoa in Public Water Supply Wells in Minnesota

Infection risk from waterborne pathogens can be estimated via quantitative microbial risk assessment (QMRA) and forms an important consideration in the management of public groundwater systems. However, few groundwater QMRAs use site-specific hazard identification and exposure assessment, so prevailing risks in these systems remain poorly defined. We estimated the infection risk for 9 waterborne pathogens based on a 2-year pathogen occurrence study in which 964 water samples were collected from 145 public wells throughout Minnesota, USA. Annual risk across all nine pathogens combined was 3.3 × 10^-1 (95% CI: 2.3 × 10^-1 to 4.2 × 10^-1), 3.9 × 10^-2 (2.3 × 10^-2 to 5.4 × 10^-2), and 1.2 × 10^-1 (2.6 × 10^-2 to 2.7 × 10^-1) infections person^-1 year^-1 for noncommunity, nondisinfecting community, and disinfecting community wells, respectively. Risk estimates exceeded the U.S. benchmark of 10^-4 infections person^-1 year^-1 in 59% of well-years, indicating that the risk was widespread. While the annual risk for all pathogens combined was relatively high, the average daily doses for individual pathogens were low, indicating that significant risk results from sporadic pathogen exposure. Cryptosporidium dominated annual risk, so improved identification of wells susceptible to Cryptosporidium contamination may be important for risk mitigation.

Peracetic acid (PAA) and low-pressure ultraviolet (LP-UV) inactivation of Coxsackievirus B3 (CVB3) in municipal wastewater individually and concurrently

Domestic wastewater (WW) contains a large number of pathogenic viruses that are not significantly reduced in most WW treatment processes and are found in high numbers in the effluent of conventionally disinfected WW. In this study, secondary WW effluent bench-scale disinfection efficacy experiments with two different peracetic acid (PAA) formulations (15 and 22% peracetic acid) and low-pressure ultraviolet irradiation (LP-UV) were carried out using Coxsackievirus B3 (CVB3) as a clinically relevant surrogate for enteric viruses and Escherichia coli (E. coli) as the disinfection efficacy control. Efficacy experiments were done in a test matrix of medium-pressure UV (MP-UV) decontaminated secondary WW effluent under representative PAA doses and LP-UV fluences used at wastewater treatment plants (WWTP). Membrane filtration technique was used to determine Log₁₀ CFU reductions of E. coli and a tissue culture infectious dose 50% assay (TCID50) for Log₁₀ TCID50 reduction of CVB3. The CVB3 proved to be quite resistant to PAA with ≤1 Log₁₀ TCID50 reduction to concentrations ≤50 mg/L at a contact time of 15 min, and highly susceptible to LP-UV at 20 mJ/cm². Concurrent use of both formulations of 3 mg/L PAA with 20 mJ/cm² LP-UV achieved ∼4 Log₁₀ TCID50 reduction. The E. coli results showed ˃5 Log₁₀ CFU reductions at a contact time of 15 min with both 3 mg/L PAA formulations, 20 mJ/cm² LP-UV treatment alone, and combined with both 1.5 mg/L PAA formulations. The E. coli efficacy data were consistent with that reported in the literature and showed to be comparable to conventional chlorine disinfection. The CVB3 efficacy data has shown that PAA alone may not be suitable for the reduction of enteric viruses in secondary wastewater effluent, but this is also the case for chlorine-based disinfectants. The results from this study showed that the use of PAA with LP-UV at reasonable concentrations (1.5 mg/L) and fluence (20 mJ/cm²) can significantly reduce the PAA use and meet wastewater disinfection goals for both E. coli and CVs. However, the concurrent use of PAA with LP-UV did not lead to significant synergy in disinfection efficacy in wastewater.

Salt Enhances the Thermostability of Enteroviruses by Stabilizing Capsid Protein Interfaces

Enteroviruses are common agents of infectious disease that are spread by the fecal-oral route. They are readily inactivated by mild heat, which causes the viral capsid to disintegrate or undergo conformational change. While beneficial for the thermal treatment of food or water, this heat sensitivity poses challenges for the stability of enterovirus vaccines. The thermostability of an enterovirus can be modulated by the composition of the suspending matrix, though the effects of the matrix on virus stability are not understood. Here, we determined the thermostability of four enterovirus strains in solutions with various concentrations of NaCl and different pH values. The experimental findings were combined with molecular modeling of the protein interaction forces at the pentamer and the protomer interfaces of the viral capsids. While pH only had a modest effect on thermostability, increasing NaCl concentrations raised the breakpoint temperatures of all viruses tested by up to 20°C. This breakpoint shift could be explained by an enhancement of the van der Waals attraction forces at the two protein interfaces. In comparison, the (net repulsive) electrostatic interactions were less affected by NaCl. Depending on the interface considered, the breakpoint temperature shifted by 7.5 or 5.6°C per 100-kcal/(mol·Å) increase in protein interaction force.IMPORTANCE The genus Enterovirus encompasses important contaminants of water and food (e.g., coxsackieviruses), as well as viruses of acute public health concern (e.g., poliovirus). Depending on the properties of the surrounding matrix, enteroviruses exhibit different sensitivities to heat, which in turn influences their persistence in the environment, during food treatment, and during vaccine storage. Here, we determined the effect of NaCl and pH on the heat stability of different enteroviruses and related the observed effects to changes in protein interaction forces in the viral capsid. We demonstrate that NaCl renders enteroviruses thermotolerant and that this effect stems from an increase in van der Waals forces at different protein subunits in the viral capsid. This work sheds light on the mechanism by which salt enhances virus stability.

Persistence of infectious Enterovirus within free-living amoebae - A novel waterborne risk pathway?

Free-living amoebae (FLA) are phagocytic protozoa found in natural and engineered water systems. They can form disinfectant-resistant cysts, which can harbor various human pathogenic bacteria, therefore providing them with a means of environmental persistence and dispersion through water distribution and other engineered water systems. The association of FLA with human viruses has been raised, but the limited data on the persistence of infectious virions within amoebae leaves this aspect unresolved. Enteroviruses can cause a wide range of illness and replicate in human respiratory and gastrointestinal tracts, both of which could be exposed through contact with contaminated waters if virus detection and removal are compromised by virion internalization in free-living protozoa. This is especially problematic for high-risk contaminants, such as coxsackieviruses, representative members of the Enterovirus genus that are likely infectious at low doses and cause a variety of symptoms to a vulnerable portion of the population (particularly infants). To investigate Enterovirus persistence within free-living amoebae we co-cultured an infectious clinical coxsackievirus B5 (CVB5) isolate, with the commonly reported tap water amoeba Vermamoeba vermiformis, after which we tracked virus localization and persistence in co-culture over time through a combination of advanced imaging, molecular and cell culture assays. Our results clearly demonstrate that infectious CVB5 can persist in all life stages of the amoebae without causing any visible injury to them. We also demonstrated that the amoeba generated vesicles containing virions that were expelled into the bulk liquid surroundings, a finding previously described for FLA-bacteria interactions, but not for FLA and human pathogenic viruses. Therefore, our findings suggest that the ability of CVB5 to persist in V. vermiformis could be a novel waterborne risk pathway for the persistence and dispersion of infectious human enteric viruses through water systems.

QMRA and water safety management: review of application in drinking water systems

Quantitative microbial risk assessment (QMRA), the assessment of microbial risks when model inputs and estimated health impacts are explicitly quantified, is a valuable tool to support water safety plans (WSP). In this paper, research studies undertaken on the application of QMRA in drinking water systems were reviewed, highlighting their relevance for WSP. The important elements for practical implementation include: the data requirements to achieve sufficient certainty to support decision-making; level of expertise necessary to undertake the required analysis; and the accessibility of tools to support wider implementation, hence these aspects were the focus of the review. Recommendations to support the continued and growing application of QMRA to support risk management in the water sector are provided.

Quantification of pathogen inactivation efficacy by free chlorine disinfection of drinking water for QMRA

To support the implementation of quantitative microbial risk assessment (QMRA) for managing infectious risks associated with drinking water systems, a simple modeling approach for quantifying Log10 reduction across a free chlorine disinfection contactor was developed. The study was undertaken in three stages: firstly, review of the laboratory studies published in the literature; secondly, development of a conceptual approach to apply the laboratory studies to full-scale conditions; and finally implementation of the calculations for a hypothetical case study system. The developed model explicitly accounted for variability in residence time and pathogen specific chlorine sensitivity. Survival functions were constructed for a range of pathogens relying on the upper bound of the reported data transformed to a common metric. The application of the model within a hypothetical case study demonstrated the importance of accounting for variable residence time in QMRA. While the overall Log10 reduction may appear high, small parcels of water with short residence time can compromise the overall performance of the barrier. While theoretically simple, the approach presented is of great value for undertaking an initial assessment of a full-scale disinfection contactor based on limited site-specific information.

Assessment of the risks for human health of adenoviruses, hepatitis A virus, rotaviruses and enteroviruses in the Buffalo River and three source water dams in the Eastern Cape

Buffalo River is an important water resource in the Eastern Cape Province of South Africa. The potential risks of infection constituted by exposure to human enteric viruses in the Buffalo River and three source water dams along its course were assessed using mean values and static quantitative microbial risk assessment (QMRA). The daily risks of infection determined by the exponential model [for human adenovirus (HAdV) and enterovirus (EnV)] and the beta-Poisson model (for hepatitis A virus (HAV) and rotavirus (RoV)) varied with sites and exposure scenario. The estimated daily risks of infection values at the sites where the respective viruses were detected, ranged from 7.31 × 10(-3) to 1 (for HAdV), 4.23 × 10(-2) to 6.54 × 10(-1) (RoV), 2.32 × 10(-4) to 1.73 × 10(-1) (HAV) and 1.32 × 10(-4) to 5.70 × 10(-2) (EnV). The yearly risks of infection in individuals exposed to the river/dam water via drinking, recreational, domestic or irrigational activities were unacceptably high, exceeding the acceptable risk of 0.01% (10(-4) infection/person/year), and the guideline value used as by several nations for drinking water. The risks of illness and death from infection ranged from 6.58 × 10(-5) to 5.0 × 10(-1) and 6.58 × 10(-9) to 5.0 × 10(-5), respectively. The threats here are heightened by the high mortality rates for HAV, and its endemicity in South Africa. Therefore, we conclude that the Buffalo River and its source water dams are a public health hazard. The QMRA presented here is the first of its kinds in the Eastern Cape Province and provides the building block for a quantitatively oriented local guideline for water quality management in the Province.

Quantitative risk assessment for food- and waterborne viruses

Quantitative microbiological risk assessment has hitherto been predominantly used for risks from exposure to bacteria. This chapter examines the requirements for full quantitative risk assessments for food- and waterborne viruses, and the interpretation and extrapolation of risk assessment outcomes. Future trends in quantitative risk assessment research for viruses are considered.

Estimating the primary etiologic agents in recreational freshwaters impacted by human sources of faecal contamination

Epidemiology studies of recreational waters have demonstrated that swimmers exposed to faecally-contaminated recreational waters are at risk of excess gastrointestinal illness. Epidemiology studies provide valuable information on the nature and extent of health effects, the magnitude of risks, and how these risks are modified or associated with levels of faecal contamination and other measures of pollution. However, such studies have not provided information about the specific microbial agents that are responsible for the observed illnesses in swimmers. The objective of this work was to understand more fully the reported epidemiologic results from studies conducted on the Great Lakes in the US during 2003 and 2004 by identifying pathogens that could have caused the observed illnesses in those studies. We used a Quantitative Microbial Risk Assessment (QMRA) approach to estimate the likelihood of pathogen-induced adverse health effects. The reference pathogens used for this analysis were Norovirus, rotavirus, adenovirus, Cryptosporidium spp., Giardia lamblia, Campylobacter jejuni, Salmonella enterica, and Escherichia coli O157:H7. Two QMRA-based approaches were used to estimate the pathogen combinations that would be consistent with observed illness rates: in the first, swimming-associated gastrointestinal (GI) illnesses were assumed to occur in the same proportion as known illnesses in the US due to all non-foodborne sources, and in the second, pathogens were assumed to occur in the recreational waters in the same proportion as they occur in disinfected secondary effluent. The results indicate that human enteric viruses and in particular, Norovirus could have caused the vast majority of the observed swimming-associated GI illnesses during the 2003/2004 water epidemiology studies. Evaluation of the time-to-onset of illness strongly supports the principal finding and sensitivity analyses support the overall trends of the analyses even given their substantial uncertainties.

Chapter 7 Global Supply of Virus-Safe Drinking Water

This chapter illustrates the recommendations and guidelines of the World Health Organization (WHO) concerning water, sanitation, and health. The recommendations and guidelines are evaluated in the light of disease caused by human pathogenic viruses. The guidelines outline a preventive management framework for safe drinking water. The framework includes health-based targets to assist national authorities who are normally responsible to set the targets for the protection of public health from risks by exposure to drinking water. Assessing the adequacy of systems, defining and monitoring control measures, and establishing management plans are the three components of the so-called water safety plans. Achievement of health-based targets may be verified by independent surveillance to assess the safety of the drinking water through additional verification or audit-based approaches. This framework for safe drinking water can be adapted according to environmental, social, economic, and cultural circumstances of drinking water provision on the national, regional, and local level. The chapter concludes that viruses could be considered as biocolloids with specific properties such as size, shape, structure, charge, composition, and genome. These viral characteristics determine their behavior in the environment, resistance to natural inactivation and treatment, and disinfection processes. For each (re-)emerging virus these properties may be known or could be assessed predicting the effectiveness of possible intervention measures for prevention of waterborne disease.

Enteroviruses and bacteriophages in bathing waters

A new procedure for detecting and counting enteroviruses based on the VIRADEN method applied to 10 liters of seawater was examined. It improved the efficiency of detection by taking into account both the number of positive isolations and numbers found with traditional methods. It was then used to quantify viruses in bathing waters. A number of bacterial indicators and bacteriophages were also tested. Cultivable enteroviruses were detected in 55% of the samples, most of which complied with bacteriological criteria. In contrast, viral genomes were only detected in 20% of the samples by reverse transcription-PCR. Somatic coliphages outnumbered all other indicators. F-specific RNA phages were detected in only 15% of the samples, whereas phages infecting Bacteroides thetaiotaomicron were detected in 70% of samples. A numerical relationship between the numbers of enteroviruses and the numbers of enterococci and somatic coliphages was observed. In situ inactivation experiments showed that viruses persisted significantly longer than the bacterial indicators. Only somatic coliphages and bacteriophages infecting Bacteroides persisted longer than the viruses. These results explain the numbers of enteroviruses and indicators in bathing waters attending the numbers usually found in sewage in the area. Somatic coliphages show a very good potential to predict the risk of viruses being present in bathing waters.

Application of microbial risk assessment to the development of standards for enteric pathogens in water used to irrigate fresh produce

Microbial contamination of the surfaces of cantaloupe, iceberg lettuce, and bell peppers via contact with irrigation water was investigated to aid in the development of irrigation water quality standards for enteric bacteria and viruses. Furrow and subsurface drip irrigation methods were evaluated with the use of nonpathogenic surrogates, coliphage PRD1, and Escherichia coli ATCC 25922. The concentrations of hepatitis A virus (HAV) and Salmonella in irrigation water necessary to achieve a 1:10,000 annual risk of infection, the acceptable level of risk used for drinking water by the U.S. Environmental Protection Agency, were calculated with a quantitative microbial risk assessment approach. These calculations were based on the transfer of the selected nonpathogenic surrogates to fresh produce via irrigation water, as well as previously determined preharvest inactivation rates of pathogenic microorganisms on the surfaces of fresh produce. The risk of infection was found to be variable depending on type of crop, irrigation method, and days between last irrigation event and harvest. The worst-case scenario, in which produce is harvested and consumed the day after the last irrigation event and maximum exposure is assumed, indicated that concentrations of 2.5 CFU/100 ml of Salmonella and 2.5 x 10(-5) most probable number per 100 ml of HAV in irrigation water would result in an annual risk of 1:10,000 when the crop was consumed. If 14 days elapsed before harvest, allowing for die-off of the pathogens, the concentrations were increased to 5.7 x 10(3) Salmonella per 100 ml and 9.9 x 10(-3) HAV per 100 ml.