Waterborne microbial risk assessment: a population-based dose-response function for Giardia spp. (E.MI.R.A study).

BACKGROUND: Dose-response parameters based on clinical challenges are frequently used to assess the health impact of protozoa in drinking water. We compare the risk estimates associated with Giardia in drinking water derived from the dose-response parameter published in the literature and the incidence of acute digestive conditions (ADC) measured in the framework of an epidemiological study in a general population. METHODS: The study combined a daily follow-up of digestive morbidity among a panel of 544 volunteers and a microbiological surveillance of tap water. The relationship between incidence of ADC and concentrations of Giardia cysts was modeled with Generalized Estimating Equations, adjusting on community, age, tap water intake, presence of bacterial indicators, and genetic markers of viruses. The quantitative estimate of Giardia dose was the product of the declared amount of drinking water intake (in L) by the logarithm of cysts concentrations. RESULTS: The Odds Ratio for one unit of dose [OR = 1.76 (95% CI: 1.21, 2.55)] showed a very good consistency with the risk assessment estimate computed after the literature dose-response, provided application of a 20 % abatement factor to the cysts counts that were measured in the epidemiological study. Doing so, a daily water intake of 2 L and a Giardia concentration of 10 cysts/100 L, would yield an estimated relative excess risk of 12 % according to the Rendtorff model, against 11 % when multiplying the baseline rate of ADC by the corresponding OR. This abatement parameter encompasses uncertainties associated with germ viability, infectivity and virulence in natural settings. CONCLUSION: The dose-response function for waterborne Giardia risk derived from clinical experiments is consistent with epidemiological data. However, much remains to be learned about key characteristics that may heavily influence quantitative risk assessment results.

Are waterborne astrovirus implicated in acute digestive morbidity (E.MI.R.A. study)?

BACKGROUND: With rotavirus and Norwalk-like viruses, astroviruses are now recognized as important etiologic agents of viral gastroenteritis in all age groups. However, astrovirus is neither routinely screened for in stool samples, nor in environmental samples, and data on the health impact of waterborne astrovirus are lacking. OBJECTIVES: To assess the potential impact of astrovirus in drinking water on the incidence of acute digestive conditions (ADC) among a panel of volunteers. STUDY DESIGN: The Epidemiology and MIcrobial Risk Assessment (E.MI.R.A.) study combined a daily epidemiological follow-up of digestive morbidity among a panel of 544 volunteers supplied by French public water systems, and a microbiological surveillance of drinking water. Cases of digestive morbidity were collected through weekly telephone calls. The bacterial, virological and parasitic quality of tap water was assessed monthly. Additional samples were collected if the incidence of ADC increased. The relationship between incidence of ADC during a 7-day period centered about the water sampling day and astrovirus RNA prevalence in drinking water was modeled by regression techniques, taking into account several confounders. RESULTS: 12% (8/68) of the analyzed water samples were positive for astrovirus, and presence of astrovirus RNA was associated with a significant increased risk of ADC: RR=1.51 (95% CI=[1.17-1.94], P value=0.002). CONCLUSIONS: This result suggests a role for waterborne astrovirus in the endemic level of digestive morbidity in the general population. Perhaps astrovirus is a candidate test target for viral surveillance of drinking water.

A new analytical tool to assess health risks associated with the virological quality of drinking water (EMIRA study).

This work assessed the risks associated with the virological quality of tapwater using a molecular analytical tool manageable in a field survey. It combined a daily epidemiological follow-up of digestive morbidity among a panel of volunteers and a microbiological surveillance of drinking water. RT-PCR was used for detection of enterovirus, rotavirus and astrovirus. 712 cases of acute digestive conditions occurred in the 544 volunteers. 38% (9/24) raw water and 23% (10/44) tap water samples were positive for at least one virus marker with 9/10 positive tap water samples complying with bacterial criteria. No statistically significant association was found between the presence of viral markers and observed incidence of digestive morbidity. However, when an outbreak occurred, enterovirus and rotavirus RNA was detected in the corresponding stored tap water samples. Sequencing of the amplified fragments showed that the rotavirus detected was of bovine origin. This work demonstrated that enteric virus markers were common in tapwater of the study communities (characterised by a vulnerable raw water) despite absence of bacterial indicators. Tangential ultrafiltration coupled to RT-PCR allowed a simultaneous and fast detection of the study viruses from environmental samples. This process is a promising tool usable for virological water surveillance, in as much the corresponding know-how is transferred to the field professionals.

[Description of drinking water intake in French communities (E.MI.R.A. study)]. / Description de la consommation d'eau de boisson dans certaines communes françaises (étude E.MI.R.A.).

BACKGROUND: Assessment of risks associated with waterborne pollutants requires a good characterization of the exposure of individuals and populations. This characterization implies knowledge of pollutants' levels in water and their time variability, and also estimation of drinking water consumption. Several studies were conducted, mostly in North America, on levels of chemical contaminants or prevalence of pathogens. Few studies were conducted on drinking water intake of the general population. METHODS: This work, included within the E.MI.R.A study which was set up to assess waterborne infectious risks, describes in details daily drinking water consumption of 544 French volunteers. Data were collected by self-questionnaires. RESULTS: RESULTS differ according to the season. Tap water usage for food follows a normal distribution (arithmetic mean in winter=1.55 l/j, 95% CI [0.20-2.90]; arithmetic mean in spring=1.78 l/j, [0.13-3.43]). Total drinking water intake follows a log-normal distribution (geometric mean in winter=1.60 l/j, standard deviation=1.73 l/j; geometric mean in spring=1.92 l/j, standard deviation=1.70 l/j). Tap water intake amounts to more than 80% of total drinking water consumption, and pure tap water (i.e not added, modified nor boiled) amounts to 42% of total drinking water. RESULTS are also displayed by age, and compared to other data available in the literature. CONCLUSIONS: This work provides data that can be used to develop risk assessment and epidemiological studies in the field of chemical or infectious risks in the context of France.