Marshall County health director says Legionella outbreak of 74 cases has ended after remediation of cooling towers

Marshall County Public Health Director Sydney Gruwell told the Board of Supervisors on Nov. 5 that a Legionellosis outbreak that began in August 2025 produced 74 confirmed cases and two deaths and is now considered over.

"Since the outbreak began in August 2025, there were a total of 74 cases of Legionellosis and 2 deaths associated with the outbreak," Gruwell said. She said the last case was reported to public health on Sept. 25 and, after two incubation periods, the outbreak was declared concluded on Oct. 23.

Gruwell said public-health teams identified 12 business centers with cooling towers in the geographic area where people were most likely infected. Each site was tested multiple times. "We did have one business center that tested positive for Legionella pneumophila serogroup 1," she said, but "it did not match the infected person that we were looking for," meaning investigators have not found a direct environmental match to patient isolates.

According to Gruwell, incident command structures at the state and local level have closed. All 12 identified cooling towers completed an "offline remediation process," which she described as shutting down the towers, performing extensive cleaning, and submitting documentation to Iowa HHS and the CDC for clearance. Gruwell said the county will continue to investigate routine Legionella reports as individual, year‑round cases rather than as part of an outbreak.

Gruwell addressed confidentiality and legal limits on disclosure. She said the identity of the business that tested positive will not be released: "That information will not be shared. It is my understanding they're protected under Iowa Code 139A for communicable disease." She added that if a business had failed to cooperate with remediation, public-health follow‑up could have produced different actions.

Board members asked whether the county can expect further regulatory changes to cooling-tower oversight. Gruwell said discussion is under way at the state level and that changes could be pursued locally (for example, by city or county ordinance), but she did not report any enacted new local regulation. She also said the state and county will publish guidance and fact sheets and that historical press releases remain available from Iowa HHS.

The public-health office will remove the outbreak-specific updates from daily website placement now that the incident is closed but will keep background disease and prevention information linked on county and state pages. Gruwell thanked local, state and federal partners and the businesses that cooperated with remediation.

Next steps: Marshall County public-health staff will monitor routine Legionella reports and link state fact sheets and cooling-tower mitigation guidance on county web and social pages.