VIRUSES IN NON-DISINFECTED GROUNDWATER USED FOR MUNICIPAL DRINKING WATER AND THE INCIDENCE OF ACUTE GASTROINTESTINAL ILLNESS
We quantified virus concentrations by real-time qPCR in the tap water of 14 Wisconsin communities that use non-disinfected groundwater as their drinking water source and related these measurements to community rates of acute gastrointestinal illness (AGI). Tap water samples were collected monthly from eight households per community and analyzed for six virus groups: enterovirus, adenovirus, hepatitis A virus, rotavirus, and norovirus genogroups I and II. AGI incidence rates were estimated from health diaries completed weekly by participating households within each study community (n = 673 households, 1,786 people). AGI surveillance and virus sampling were conducted for four three-month periods. AGI incidence was related to virus concentrations using Poisson regression with random effects.
Among 1,204 tap water samples from 14 communities, 287 (24%) were positive for at least one virus type and 41 (3%) were positive for two or more types. The most frequently detected types were adenoviruses, enteroviruses, and GI noroviruses. Concentrations of enteroviruses and G1 noroviruses were on the order of ones to hundreds genomic copies/liter, whereas adenovirus concentrations were one or two orders of magnitude lower. The arithmetic mean and maximum concentration of total viruses in the communities’ tap water was positively associated with AGI (P-values = 0.009 and 0.004, respectively). The association between AGI and virus level was particularly significant for GI norovirus and between adult AGI and enterovirus when echoviruses predominated. No relationship was found between AGI and adenoviruses. AGI relative risk increased by 30% at mean concentrations of GI norovirus and enterovirus of 1 and 0.8 genomic copies/L, respectively. Using quantitative microbial risk assessment, the fraction of AGI in the communities that was attributable to drinking non-disinfected groundwater could have been as high as 22%.
As many public water systems in the United States rely on non-disinfected groundwater, when virus contamination occurs waterborne disease transmission can be significant.