Why Legionnaires’ Disease Cases Are Rising in Michigan

What’s driving the rise of Legionnaires' Disease in Michigan? Have you seen recent cases reported across the state?”

Turns out, Legionella bacteria are more common than most people realize, but the disease itself is relatively rare. Here's what you should know about Legionnaires' Disease in our state:

First, what is Legionnaires' Disease?

I think the first time I ever heard about Legionnaires' Disease was probably on a show like Unsolved Mysteries or Forensic Files, because the way the disease was discovered was quite peculiar:

In 1976, members of the American Legion (hence the name Legionnaires' Disease) attended a convention at the Bellevue-Stratford Hotel in Philadelphia. Dozens of them fell mysteriously ill, and 29 ultimately people from the incident. As for the cause? Investigators were stumped.

Eventually the source of the spread was linked to contaminated hotel air conditioning and water systems which were harboring this unknown (at the time) bacterium. According to research database EBSCO,

The causative agent, Legionella pneumophila, was not identified until January 1977, complicating the initial investigation as it mimicked other illnesses and could not be cultured through standard laboratory methods. This bacterium is now acknowledged as a major cause of community-acquired pneumonia, particularly affecting older adults and those with compromised immune systems.

Recent Legionnaires' Cases in Michigan:

On January 27, 2026, Bronson Methodist Hospital in Kalamazoo confirmed a case of Legionnaires' Disease which prompted an investigation with state health officials. Kalamazoo's WWMT reported,

Bronson said the patient was diagnosed New Year's Eve and that they are investigating potential exposure with several medical officials...In the meantime, Bronson has taken several precautionary measures. They include micro filters on shower heads, removing sink aerators, installing mixing valves to control water temperature, and placing restrictions on showering.

Now, we're learning Legionella has been found in two Oakland County buildings with water quality testing now underway at the Oakland County Jail, as well. Per Detroit's 7 WXYZ,

Legionella bacteria was discovered inside the Sheriff's office building 38E in early December...The 7 Investigators previously reported Oakland County did not have a plan to routinely test its water system inside its buildings. A custodial employee was recently diagnosed with Legionnaires' disease, revealing the presence of Legionella bacteria in the Oakland County Sheriff’s Office headquarters.

So, Why the Recent Rise in Cases?

In short, we don't know. These cases in Oakland County and Kalamazoo are most likely unrelated incidents as the most common way to contract Legionnaires' Disease is by breathing in droplets containing the bacteria. Per the U.S. Centers for Disease Control (CDC),

In general, it isn't spread person to person.

Legionella exists in nature and can be found in freshwater environments but are typically low enough in numbers and don't usually cause a threat to humans. However, Legionella can be dangerous when it grows in large man-made water systems which may have warm, stagnant water inside.

That got me thinking, could my household humidifier be harboring Legionella? Absolutely!

The CDC recommends emptying and drying your household humidifiers regularly, especially those with a cool-mist function as the water does not get warm enough to prevent the growth of Legionella like warm mist humidifiers typically do. Other common items that may harbor Legionella:

• CPAP machines
• ice machines
• produce and recreational misters (like at amusement parks)

For more information on how to prevent Legionella growth and the symptoms of Legionnaires' Disease, click here.