In June 2021, the Pennsylvania Department of Health investigated an outbreak of E. coli O157:H7 infections among patrons of a community swimming pool. Fifteen cases (9 confirmed, 6 probable) were identified. All persons reported swimming at the pool on May 31, 2021, the seasonal opening date. They had no other common exposures. Symptom onsets occurred between June 2-June 4, 2021. Six patients were hospitalized. None developed hemolytic uremic syndrome. No one died.

Pool inspection revealed an automatic chlorinator malfunction. Record keeping was inconsistent with local requirements, and few available records demonstrated at least one instance of no detectable chlorine. After closing on June 7, the pool reopened following chlorinator repair, after which no additional cases were identified.