Health officials across the state are trying to determine what's causing a 143% increase in cases of Legionnaires' Disease, a respiratory infection that can be deadly, especially for people with weak immune systems.

"In the warm months, there is an increase in Legionnaires'," said Jennifer Eisner of the Michigan Department of Community Health. "At this point no common source has been identified."

In June and July of this year, 73 cases have been confirmed. In the past three years, the average number of cases during those months was 30.

Eisner said state health officials are working with counties to try to address the problem.

The disease is caused by the Legionella bacteria that is typically transmitted in water vapor. Symptoms include fever, cough, and pneumonia. Eisner said the state also has seen cases of Pontiac fever, a similar, though milder, infection that doesn't include pneumonia that resolves on its own.

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Legionella bacteria are found naturally in fresh water lakes and streams, but can also be found in man-made water systems. Cooling towers, hot tubs and decorative fountains can allow bacteria growth and transmission if they are not cleaned and maintained properly, Eisner said.

Transmission to humans occurs when mist or vapor containing the bacteria is inhaled. Legionellosis does not spread from one person to another.

State health officials say risk factors for exposure to Legionella bacteria include:

  • Recent travel with an overnight stay outside of the home
  • 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. Seniors, current and former smokers, people with lung diseases and people with compromised immune systems face the greatest risks.

More information is available on the website of the Centers for Disease Control.

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