LANSING, Mich. – The Michigan Department of Health and Human Services (MDHHS) is coordinating with local health departments across the state to investigate cases of legionellosis this summer. To date in 2018, there have been 135 confirmed cases of legionellosis reported in 33 counties compared to 107 confirmed cases during the same timeframe in 2017.

Confirmed cases include 24 in the City of Detroit, 19 in Macomb County, 16 in Oakland County, 11 in Wayne County and 10 in Genesee County. Twenty-four of the cases have been confirmed statewide since July 1, and another 13 cases are pending confirmation.

This increase corresponds with national increases in legionellosis. Legionellosis is most common in the summer and early fall when warming, stagnant waters present the best environment for bacterial growth in water systems.

MDHHS and local health departments are working to inform healthcare providers of the increase in cases and share information regarding testing and treatment. Legionellosis is a respiratory infection caused by Legionella bacteria. Legionnaires’ disease is an infection with symptoms that include fever, cough and pneumonia. A milder form of legionellosis, Pontiac fever, is an influenza-like illness without pneumonia that resolves on its own.

Legionella bacteria are found naturally in fresh water lakes and streams but can also be found in man-made water systems. Potable water systems, cooling towers, whirlpool spas and decorative fountains offer common environments for bacterial growth and transmission if they are not cleaned and maintained properly. Warm water, stagnation and low disinfectant levels are conditions that support growth in these water systems.

Transmission to people occurs when mist or vapor containing the bacteria is inhaled. Legionellosis does not spread person to person. Risk factors for exposure to Legionella bacteria include:

  • Recent travel with an overnight stay.
  • Recent stay in a healthcare facility.
  • Exposure to hot tubs.
  • Exposure to settings where the plumbing has had recent repairs or maintenance work.

Most healthy individuals do not become infected after exposure to Legionella. Individuals at a higher risk of getting sick include the following:

  • People over age 50.
  • Current or former smokers.
  • People with chronic lung disease.
  • People with weakened immune systems from diseases, such as cancer, diabetes or liver or kidney failure.
  • People who take immunosuppressant drugs.

Individuals with any concerns about Legionnaires’ disease or exposure to the Legionella bacteria should talk to their healthcare provider. MDHHS and local health departments will continue to monitor cases and provide updates to the public. More information on Legionella and Legionnaires’ disease can be found on the Centers for Disease Control and Prevention website.


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