Household Well Study Following Illness with Reportable Enteric Infections

BACKGROUND: Over 15 million United States households rely on private well water as their primary source of water. While public water supplies are regularly monitored, once construction is complete, the owner of a private well is typically responsible for maintaining the well and monitoring well quality, condition, and performance. Groundwater consumption is a known risk factor for infections with a number of enteric pathogens. Much of southeastern Minnesota, where many residents rely on private wells for their drinking water, is comprised of karst aquifers where the groundwater is more vulnerable to contamination. We examined the association between private well water contamination and enteric illness. Factors associated with private well water bacterial contamination were also assessed.

METHODS: We conducted a case-control study during May-October in nine counties in southeastern Minnesota. Eligible cases were residents of the study counties who had a laboratory-confirmed Campylobacter, Cryptosporidium, or STEC infection and who reported well water during their exposure period. Up to three control households were recruited for each case using a reverse-directory of addresses in the vicinity of the case’s home. During the initial phone interview, detailed information about the well was collected using a standard questionnaire. The site visit included recording the GPS location of the well, performing an evaluation of potential contaminants surrounding the well, and taking a water sample from the kitchen faucet.

RESULTS: A total of 31 eligible cases were identified during the study period; 24 (77%) agreed to participate. Overall, 28 (30%) household kitchen faucets tested positive for total coliforms, including 8 (33%) cases and 20 (29%) controls. Being unable to locate a well log, either through the property owner or the Minnesota Well Index (21 of 28 coliform positive vs. 18 of 64 coliform negative; p<0.001) or having an animal or poultry building within 50 feet of the well (6 of 28 coliform positive vs. 1 of 64 coliform negative; p=0.003) were independently associated with a coliform-positive kitchen faucet.

CONCLUSIONS: Private wells in southeastern Minnesota were frequently contaminated with coliform bacteria, regardless of whether someone in the household had recently been ill with an enteric illness. Owners of private wells are responsible for the maintenance and safety of their drinking water. At a minimum, private wells should be tested for coliform bacteria once a year; old wells or wells less than 50 feet deep should be tested more frequently.