State: Source of 34 Legionnaires’ disease cases in Marshalltown likely a cooling tower

MARSHALLTOWN — The number of Legionnaires’ disease cases among Marshalltown residents was up to 34 on Tuesday, as public health officials work to identify the source of the outbreak, State Epidemiologist Dr. Matthew Donahue told the Marshall County Board of Supervisors on Wednesday.

Last Thursday, the state reported there had been 21 cases of Legionnaires’ disease diagnosed in Marshalltown, and one death. All of the cases were in people living in the north central part of the city, Iowa Health and Human Services said.

Legionnaires’ disease is caused by Legionella bacteria, which thrive in warm water and typically spread when a person inhales aerosolized water droplets.

Normally, Donahue told the supervisors, Legionella is found in freshwater environments like ponds, lakes, rivers, soil and gardens.

“... when it’s in those places, it doesn’t cause a problem, but it really, really likes warm water. And Legionella can grow to higher levels when it finds warm water and a manmade system — something like a cooling tower, something like a water fountain or something like a hot tub,” Donahue said.

Cooling towers, he noted, are used in industrial settings for buildings that have a lot of warm water due to a large air conditioning system to remove heat from the system and pool water at the top of the building. Cooling towers bring hot water from the building up and use evaporation to get rid of it.

If Legionella makes its way into the system, it can multiply to high levels, and the evaporation can spread the bacteria into the air.

Legionnaires’ disease can cause severe pneumonia in people, but it is treatable with antibiotics.

Because the bacteria are “everywhere,” most people who are exposed to it do not get sick at all, but those at the highest risk are people who are older, have smoked or have other medical conditions.

“One main message that I think we’ve talked about already is that anyone in the Marshalltown area who gets sick with a pneumonia like system with a respiratory illness should talk to their doctor about Legionella. It’s something we can test for really easy. It’s something that’s very treatable with antibiotics, and that’s been a core message we hope to get across,” Donahue said.

Donahue said HHS began to investigate as soon as a cluster of Legionnaires’ disease cases was identified in Marshalltown. He said state officials and Marshall County Public Health Director Sydney Grewell have been in “constant contact” while receiving assistance from the Centers for Disease Control and Prevention (CDC).

“We’re trying to figure out exactly how people are getting sick with Legionella here, so we don’t have all the answers yet. But we are starting to hone in on a top hypothesis,” Donahue said. “It doesn’t look like this is coming from a hotel. It doesn’t look like this is coming from a water fountain. It doesn’t look like it’s coming from a hot tub. It’s most likely coming from a cooling tower.

“We don’t have a smoking gun,” he added. “We might not find a smoking gun that tells us exactly how this happened, but because of how wide it appears to be spread, because of the calls we made to patients so far, that seems like the most likely answer.”

So far, officials have tested nine of the cooling towers they believe could be responsible for the outbreak, though later in Wednesday’s meeting, Donahue sidestepped a question about where the towers are located, and declined to answer directly. He reiterated that the tests may not provide a firm answer, comparing them to a strep throat culture.

County and state officials are asking businesses to disinfect their cooling towers, which will kill the Legionella and decrease the risk of it spreading further. As of Wednesday morning, four had completed the disinfection process, and Donahue expressed confidence that the others would do the same.

Answering questions from the county supervisors, Donahue said Legionnaires’ disease does not spread person-to-person. Grewell added that it also doesn’t come from drinking water.

One supervisor asked Donahue whether it’s safe for people to visit Marshalltown. Donahue responded that he was excited to be in the community on Wednesday.

“I wouldn’t cancel a plan to visit Marshalltown. I wouldn’t not go out to eat at a restaurant or visit a local shop because of the outbreak that’s happening now from Legionella, especially with as far as we’ve gotten at this point,” Donahue said.

Supervisors also asked about regulation of cooling towers, and how a future outbreak could be prevented

Grewell said that as she visits cooling towers to test for Legionella, she has shared information about regular tower cleaning. Some of the businesses, Grewell said, have committed to stepping up their cooling tower maintenance.

Donahue added that anyone with a cooling tower should have a water management plan that ensures regular disinfection.