A Campylobacter Outbreak from Livestock Wastewater in a Town's Wells, Nebraska, 2017

In March 2017 the Nebraska Department of Health and Human Services and the Southwest Nebraska Public Health Department learned of an unusual cluster of Campylobacter jejuni infections in a small town, called city A. Campylobacter has caused outbreaks linked to poultry, unpasteurized milk and contaminated water. City A draws its water from four untreated wells feeding one connected system.

A cluster appears

On March 10 the state was notified of five campylobacteriosis reports in the district among people who did not live together — two from stool cultures and three from a gastrointestinal PCR panel, a culture-independent test. From 2006 to 2016, city A had averaged about one Campylobacter case every 3 years. Early interviews did not ask about untreated drinking water and pointed to ground beef, but tracing poultry and ground beef supplied to two local restaurants and a grocery store found no shared source. Then residents and business owners mentioned standing water that smelled of cattle manure in a roadside ditch near two city wells.

What went wrong

A center-pivot irrigation system was pumping a large volume of wastewater from a concentrated animal feeding operation onto neighboring farmland — a common way to fertilize and water crops. At some point it malfunctioned, and runoff flooded a road ditch about 15 feet (4.6 m) from the well houses of wells 3 and 4. City operators saw water in the ditch February 22–25, and on February 24 watched livestock wastewater flowing into the ditch near well 4 from farmland upstream.

• Well 3 was pumping February 22–27 and well 4 February 28–March 7, each alongside well 2; operators rotate wells routinely.
• The water received no disinfection or filtration.
• Wells 3 and 4 were shallow — static water levels of 21 and 22 feet and total depths of 43 and 46 feet — and, like the other wells, dated from the 1930s.
• Routine coliform and E. coli testing on March 8 happened to cover only wells 2 and 5, and later tests of all four wells in mid- to late March, including cultures for Campylobacter, were negative.

Finding the cases

An online questionnaire went to the town of about 600 people; 94 (16%) responded. Among them, 39 cases (6 confirmed, 33 probable) were identified, with illness starting February 28–March 21: 25 women and 14 men, median age 34.5 (range 1.5 to 85). Twelve (31%) sought medical care and three (8%) were hospitalized; no one died.

Drinking untreated, unboiled city tap water was the only exposure significantly linked to illness (odds ratio 7.84; 95% confidence interval 1.69–36.36). Unpasteurized milk, animal contact, raw poultry and ground beef were not. None of the roughly 28 residents of the town's only nursing home fell ill; it used city water but treated it by reverse osmosis.

Confirmed and probable cases by date of illness onset, with the dates each well was pumping. CDC.

The response

Wells 3 and 4 were permanently taken out of service on March 16, and no one fell ill after March 21. On April 25 the state reclassified them to emergency status, usable only for non-drinking purposes in emergencies such as fires or drought, and the findings supported a planning grant for a new, deeper, higher-volume well in a different location.

Lessons

• Environmental and statistical evidence, and past outbreaks of similar size, point to contaminated water as the cause, even though water tests were negative — samples were taken long after the event, wells had been switched, routine coliform tests may not signal Campylobacter, and the bacteria may survive in water without growing in culture.
• Culture-independent tests made the difference: culture alone would have found only two cases, one in a non-resident and one with a typical poultry exposure, and might not have triggered a fast response.
• Investigators should ask early about untreated water as a possible source of Campylobacter outbreaks. Clean water access remains an important public health issue.

Sources

Based on Pedati C, Koirala S, Safranek T, Buss BF, Carlson AV, "Campylobacteriosis Outbreak Associated with Contaminated Municipal Water Supply — Nebraska, 2017," MMWR Vol. 68, No. 7, CDC; a work of the United States government in the public domain.