Marshall County public health reports 74 Legionella cases, two deaths; no new cases in nearly two weeks

Marshall County Public Health Director Sydney Gruwell told the Board of Supervisors on Oct. 8 that the county has identified 74 Legionella cases and two deaths connected to a local outbreak. “As of this morning, we have identified 74 cases and 2 deaths related to the outbreak,” Gruwell said.

Gruwell said the last positive case came on Sept. 25, meaning the county has not recorded a new case in nearly two weeks. “Our last positive case was reported on September 25, which tomorrow will mark 2 weeks,” she said, and added that the absence of new positives is consistent with remediation efforts.

Investigators focused on cooling towers in northern Marshalltown and identified 12 business centers with towers that underwent repeated testing; one business center tested positive for Legionella pneumophila serogroup 1 but that strain did not match the patient sequence investigators sampled. Gruwell said finding Legionella in a tower supports the cooling‑tower theory even when sequencing does not produce a direct match.

“Each business center has been tested multiple times,” she said. “Two of those businesses have completed full offline remediation, which is completing the full disinfection process.” Gruwell said businesses began additional disinfection work in mid‑September and that the pause in new cases makes completing offline remediation important.

Gruwell explained that Legionella is a reportable disease in Iowa and that laboratories and health care providers must report positive test results to Iowa HHS and the relevant local health department via electronic lab reporting. Case counts for this outbreak reflect people who meet the county’s case definition — including residence, work or presence in the north‑central Marshalltown area during the exposure window — and are updated on the Iowa HHS website.

Gruwell noted Iowa does not require a cooling‑tower registry or routine state inspection program like some states do; she said the towers’ owners are responsible for water‑management plans and ongoing monitoring. “We don’t have in Iowa any form of regulation,” she said, adding that New York, for example, requires tower registration.

The county update did not assign a final source by sequencing for all cases. Gruwell urged businesses that own cooling towers to maintain water‑management plans and complete remediation steps to reduce future risk. The board did not take formal action during the update; members asked questions about testing, reporting and whether cases might be missed, and Gruwell described the reporting and case‑definition process that governs inclusion in the outbreak count.

The next procedural step is continued monitoring and follow‑up with businesses undergoing remediation. Marshall County Public Health and Iowa HHS will continue to update the public through routine reporting channels.