Submitted to: Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/27/2012
Publication Date: 7/27/2012
Citation: Lambertini, E., Borchardt, M.A., Kieke, B.A., Spencer, S.K., Loge, F.J. 2012. Risk of viral acute gastrointestinal illness from non-disinfected drinking water distribution systems. Environmental Science and Technology. 46:9299-9307. Interpretive Summary: There are two basic routes by which contaminants can reach drinking water: 1) the water source is contaminated; and 2) the pipes distributing the water allow contaminants to enter. For the second route, there is growing evidence that, even when drinking water pipes are under positive pressure, contaminants can enter through backflows, through pipes incorrectly connected to wastewater pipes, and through leaks when the water pressure becomes negative for a short time. The research question we addressed is: how many infectious illnesses result from pathogens directly entering the distribution system pipes of municipal water systems that do not practice disinfection? We installed ultraviolet light disinfection (UV) on the groundwater wells of 14 Wisconsin communities. The UV killed all pathogens in the well, eliminating the first route of drinking water contamination, the water source. Unlike a chemical disinfectant such as chlorine, the UV disinfectant does not stay in the pipes. Thus, pathogens entering the pipes would not be killed and we could measure their concentrations in the distribution systems by sampling downstream from household tap water. We then used dose-response relationships to convert the pathogen concentrations in the distribution systems to rates of gastrointestinal illness in the communities. We estimated about 0.03 episodes of acute gastrointestinal illness per person per year were related to human viruses entering the water distribution system pipes; the exact illness rate depended on the dose-response relationship selected. Considering all the transmission routes of pathogens leading to acute gastrointestinal illness (food, contact with family members, etc.), the proportion of illness related to drinking water distribution systems in these communities was about 2%. However, considering only drinking water as the transmission route, where the source of contamination is from either the groundwater source or the distribution system, the latter was responsible for approximately 30% of drinking waterborne disease in the communities. Maintaining water distribution system infrastructure and using a continuous disinfectant in the pipes would help reduce the number of illnesses from distribution system contamination.
Technical Abstract: Acute gastrointestinal illness (AGI) resulting from pathogens directly entering the piping of drinking water distribution systems is insufficiently understood. Here, we estimate AGI incidence attributable to virus intrusions into non-disinfecting municipal distribution systems. Viruses were enumerated in the water of 14 groundwater community water systems. Each community received ultraviolet (UV) disinfection at wellheads during one study year, and no treatment during the other year. Water samples were collected monthly at wells and households during four three-month periods in 2006-07. For both UV intervention and non-intervention periods, a Monte Carlo risk assessment framework was used to estimate AGI risk from distribution systems using study-specific exposure-response relationships. Virus intrusions were observed in 12 of 13 systems, as evidenced by viruses increasing between the point of UV disinfection and household taps. Depending on the exposure-response relationship selected, AGI risk attributable to the distribution systems was 0.0180-0.0661 episodes/person-year during UV intervention, and 0.0011-0.1047 during non-intervention. These values represented 0.1-4.9% of AGI risk from all exposure routes, and 1.6-68% of risk attributable to drinking water. AGI risk was highly variable, reflecting the sporadic nature of contamination events. Virus intrusions into non-disinfected drinking water distribution systems can contribute to sporadic AGI.