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With warmer months approaching, cases of Legionnaires' disease possible


LANSING, Mich. – While Legionnaires’ disease can happen at any time of the year, it is more common during warmer months when temperatures are ideal for growth of the bacteria that cause this disease (Legionella).  That is why more people tend to get Legionnaires’ disease in the summer and fall. 

"To continue the joint efforts to protect the health of residents of the city of Flint, the Michigan Department of Health and Human Services and Wayne State University are working to ensure that residents are aware of the potential for disease spread as the warmer months approach,” said Dr. Eden Wells, chief medical executive with the MDHHS.

Legionella is a type of bacteria commonly found in the environment that grows best in warm water, such as hot tubs, cooling towers, hot water tanks, drinkable water systems, and decorative fountains. When people are exposed to the bacteria, it can cause Legionnaires’ disease, a respiratory disease that can infect the lungs and cause pneumonia. In general, Legionnaires’ disease is not spread from one person to another. However, this has been documented in extremely rare cases.

Most healthy people do not get sick after being exposed to Legionella. Being 50 years or older or having certain risk factors increases the chances of getting sick. Other risk factors include being a current or former smoker; having chronic lung disease, such as emphysema or chronic obstructive pulmonary disease; having a weakened immune system from diseases like cancer, diabetes, or kidney failure; or taking medicine that weakens your immune system. Legionnaires’ disease in children is not common.

MDHHS and WSU are issuing this statement because Genesee County had increased cases of Legionnaires’ disease in 2014 and 2015. MDHHS cannot conclude that these increases were related to the water switch in Flint nor can we rule out a possible association at this time.

Looking ahead to the coming warmer months, MDHHS is working with buildings with large water systems such as hospitals and nursing homes, hotels and motels, and buildings with more than 10 stories to help protect people from Legionnaires’ disease. The U.S. Centers for Disease Control and Prevention has been working with MDHHS in identifying buildings at increased risk for Legionella growth and spread and developing tools to support Legionella prevention. Further, chlorine (a water disinfectant that inhibits Legionella growth) levels will continue to be closely monitored throughout the municipal system.

“As part of the U.S. Government response in Flint, we are collaborating with MDHHS and the Genesee County Health Department to make sure as many Legionnaires’ disease cases as possible are prevented in the future,” said Nancy Messonnier, Deputy Director of CDC’s National Center for Immunization and Respiratory Diseases.

Additionally, WSU has developed a protocol that includes rapid interviewing of patients reported with Legionella infections, promotion of appropriate specimen collection, and testing for Legionella and chlorination levels in the homes of people who are confirmed to have Legionnaires’ disease. Testing will help us understand if the water treatment process is adequate. 

Finding Legionella in a water system is not uncommon. Studies have shown that Legionella bacteria can be found in anywhere from 6 to 33 percent of sampled homes, however, even if it is found, the risk of the average person acquiring Legionnaires’ disease from their home water system is very low. If Legionella is found in someone’s home, we will be able to compare those specimens with the clinical specimens from the patient to try to understand where the patient’s infection came from, as well as work with residents who have Legionella detected in their homes to improve the safety of their water.

For any resident that develops pneumonia symptoms, you should see a doctor right away. Signs and symptoms of pneumonia can include cough, shortness of breath, muscle aches, headache, and high fever. Be sure to tell the doctor if you have used a hot tub, spent any nights away from home, or stayed in a hospital in the last two weeks. Legionnaires' disease requires treatment with antibiotics, and most cases can be treated successfully.

For more information about Legionnaires’ disease, visit

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