As the swim season takes off in earnest, it remains crucial to ensure that commercial pools are properly maintained, equipment in tip-top shape, and sanitizer levels at recreational facilities tested and results recorded frequently.

The people who maintained a Pennsylvania community pool learned this the hard way when more than a dozen children were sickened and required medical care after becoming infected by both E. coli and C. difficile last summer.

According to a May, 2022, field report from the Centers for Disease Control, on June 7, 2021, the Pennsylvania Department of Health received numerous complaints of gastrointestinal illness from patrons who had visited a community swimming pool. Two patrons reported positive Shiga toxinproducing Escherichia coli (STEC) and Clostridioides difficile from stool specimens. The department ordered the pool closed and initiated an outbreak response to identify the source and prevent additional illnesses.

Fifteen cases were identified in children ages 4-14 who had visited the pool on its opening date, May 31. Nine cases were confirmed, and six were probable.

Probable cases were defined as three or more loose stools in 24 hours with nausea, vomiting, fever, or cramps. Thirteen patients sought medical evaluation, and six were hospitalized. Four received antibiotics for C. difficile. None developed severe complications which can cause kidney failure.

The source of the outbreak was initially mysterious because both of the bacteria responsible for causing the illnesses are readily killed by chlorine. However, inspection of the equipment at the pool revealed an automatic chlorinator malfunction. Furthermore, record-keeping was inconsistent with local requirements, and the few available records demonstrated at least one instance of no detectable chlorine.

Following chlorinator repair, the pool was reopened, after which no additional cases were identified.

According to Dr. Marc Siegel, a clinical professor of medicine at NYU Langone Medical Center in New York City, the outbreak could have been prevented if the pool’s chlorine had been maintained at recommended levels and the pool had adequate filtration.

“Also, people entering pools should shower first, which almost nobody does,' Siegal said.