Legionnaires' Disease Lawyer

November 7, 2025 — Marshall County, Iowa

After weeks of investigation and dozens of confirmed cases, Marshall County Public Health (MCPH) has officially declared the Legionnaires’ disease outbreak over. But despite extensive testing and cooperation with the Centers for Disease Control and Prevention (CDC), officials say the precise source of the bacteria was never found.

The outbreak, which began in early September, sickened 74 people and led to two deaths. Health officials identified 12 business centers in north-central Marshalltown as likely locations where exposure may have occurred — all of which contained cooling towers, a common source of Legionella bacteria.

Each facility underwent repeated testing. Only one business center tested positive for Legionella pneumophila serogroup 1, the strain known to cause Legionnaires’ disease. However, that strain did not genetically match the samples taken from infected patients.

“We still don’t have the smoking gun, and we may not ever find the smoking gun,” the department said in a statement. “But the fact that we found Legionella at all means we were on the right track.”

Six Weeks Without a Case

The last confirmed case was reported on September 25. By October 23, the county had passed two full incubation periods — the threshold for declaring the outbreak over.

Since then, no new infections have been identified, which officials attribute to the aggressive disinfection and remediation measures taken at affected facilities. Ten of the twelve sites have already completed full offline remediation — an intensive process involving system shutdown, deep cleaning, and disinfection — with the remaining two expected to finish before reopening.

“The fact that we haven’t seen a case in six weeks means the disinfection process is working,” MCPH said. “Completing full remediation ensures the bacteria is cleaned out for good.”

Routine Risk Remains

With the official end of the outbreak, Marshall County will no longer treat any new Legionnaires’ cases as part of this cluster. Going forward, any future cases will be among the 30–70 incidents typically reported in Iowa each year.

The Iowa Department of Health and Human Services will also discontinue its special outbreak updates on its website.

Even though the investigation ends without a clear culprit, the incident underscores the ongoing public-health challenge of managing Legionella risks in cooling towers and other large water systems — especially as climate change and aging infrastructure increase vulnerability across the Midwest.