Quantitative microbial risk assessment of distributed drinking water using faecal indicator incidence and concentrations

Abstract

Quantitative Microbial Risk Assessments (QMRA) have focused on drinking water system components upstream of distribution to customers, for nominal and event conditions. Yet some 15-33% of waterborne outbreaks are reported to be caused by contamination events in distribution systems. In the majority of these cases and probably in all non-outbreak contamination events, no pathogen concentration data was available. Faecal contamination events are usually detected or confirmed by the presence of E. coli or other faecal indicators, although the absence of this indicator is no guarantee of the absence of faecal pathogens. In this paper, the incidence and concentrations of various coliforms and sources of faecal contamination were used to estimate the possible concentrations of faecal pathogens and consequently the infection risks to consumers in event-affected areas. The results indicate that the infection risks may be very high, especially from Campylobacter and enteroviruses, but also that the uncertainties are very high. The high variability of pathogen to thermotolerant coliform ratios estimated in environmental samples severely limits the applicability of the approach described.Importantly, the highest ratios of enteroviruses to thermotolerant coliform were suggested from soil and shallow groundwaters, the most likely sources of faecal contamination that are detected in distribution systems. Epidemiological evaluations of non-outbreak faecal contamination of drinking water distribution systems and thorough tracking and characterisation of the contamination sources are necessary to assess the actual risks of these events.

Rapid Concentration and Molecular Enrichment Approach for Sensitive Detection of Escherichia coli and Shigella Species in Potable Water Samples

“…The implementation of molecular methods could represent a suitable avenue for such tests (14). However, the application of rapid molecular testing to the monitoring of the microbiological quality of potable water is lagging, mainly due to the scarcity of simple technological solutions for tackling the major task of efficiently concentrating and recovering as little as one microbial particle (indicator and/or pathogen) from a water sample (32).…”

Molecular Method for Detection of Total Coliforms in Drinking Water Samples

“…Indeed, the primers used must be capable of detecting all coliform members but not noncoliform bacteria. Furthermore, the application of molecular testing to the microbiological quality of potable water is far from commonplace due to the scarcity of simple technological solutions for tackling the major task of efficiently concentrating and recovering as little as one microbial particle (indicator and/or pathogen) from a water sample (11).…”

Improving Environmental Sanitation, Health, and Well-Being: A Conceptual Framework for Integral Interventions

“…This allows, accordingly, the assessment of CCPs in food chains (production, transformation, and consumption) and sanitation systems (Haas et al, 1999). This methodology has been more and more used in risk assessment of drinking water (Howard et al, 2006;van Lieverloo et al, 2007) and other practices, such as waste management (Westrell et al, 2004;Eisenberg et al, 2008). Recently, QMRA has been used to assess the risk of infection resulting in high risk of diseases for the population in contact with wastewater (Mara et al, 2007;Seidu et al, 2008).…”