CHICAGO - The Chicago Department of Public Health reported today an increase in cases of Legionnaires’ disease in the city this month. In the first three weeks of July (1-21), 49 cases of Legionnaires’ disease were reported in Chicago, which is about a 3-fold increase in cases compared to the same period in 2020 (16 cases) and 2019 (13). Among the 49 people with Legionnaires’ disease to date in 2021, 15 (31%) were admitted to the ICU and two individuals died.

CDPH issued an alert to local healthcare providers on July 9 reporting this increase in cases. A similar increase in illness has also been reported in Michigan. CDPH is investigating to find any common geographic or facility exposures. Legionnaires’ disease follows a seasonal pattern in Chicago, with an increased number of cases reported from June to October each year.

Prolonged building shutdowns or periods of limited use, as seen with COVID-19, can allow Legionella bacteria to grow and multiply in water systems. Legionella bacteria are found naturally in freshwater lakes and streams but can also be found in man-made water systems. Warm water, stagnation, and low disinfectant levels can support growth in these water systems. Potable water systems, cooling towers, whirlpool spas and decorative fountains should be cleaned and maintained properly to prevent bacterial growth and spread.

Weather patterns including temperature, humidity, and precipitation have been shown to be associated with increased Legionnaires’ disease. Healthcare providers should remain vigilant and send sputum for culture and polymerase chain reaction (PCR) testing in addition to the urine antigen test for diagnosis and treatment appropriately.

To date, no common sources of infection have been identified. CDPH continues to investigate cases and will provide updates if any common source is identified.

“This is a reminder to keep your water systems flushed and clean. Those with risk factors should seek care early if they develop symptoms, and clinicians should do appropriate testing and treat empirically,” said CDPH Commissioner Allison Arwady, M.D.

Legionnaires' disease is caused by Legionella bacteria which live naturally in fresh-water. People can get Legionnaires’ disease when they breathe in water droplets containing the bacteria. It is not typically spread person-to-person. Symptoms of the illness include cough, shortness of breath, fever, muscle aches, and headaches. Most healthy people exposed to Legionella bacteria do not get sick, but people over 50-years-old, current or former smokers and people with chronic lung disease or weakened immune systems are at increased risk of Legionnaires’ disease.

People at high risk should see a doctor as soon as possible if they are experiencing unusual respiratory symptoms. Wear a mask when visiting a healthcare provider as these symptoms are also seen with COVID-19.