The Illinois Department of Public Health (IDPH) is investigating two clinical cases of Legionnaires’ disease in individuals who were both patients at the University of Chicago Medical Center.  The investigation is currently limited to this facility; the general public is not at risk. IDPH is working with the Chicago Department of Public Health (CDPH) and the hospital to collect information and further investigate these cases, including an on-site joint visit by IDPH and CDPH this week to test the facility’s water.  The hospital has reported to public health officials that it conducts extensive testing of its water and those test results have been negative for the Legionella bacteria.  The individuals were patients at the hospital for part of the time when they could have been exposed to the bacteria. Both individuals also received care elsewhere during the same period. The facility has worked with IDPH and has already provided information to impacted patients and families about Legionella. Legionella bacteria occur naturally in the environment.  Water containing Legionella can be aerosolized through cooling towers, showers, hot tubs, and decorative fountains, and can cause Legionnaire’s disease, a serious lung infection (pneumonia) when inhaled.  Legionnaires’ disease is not passed from person to person.  Outbreaks are most commonly associated with buildings or structures that have complex water systems like hotels, hospitals, long-term care facilities, and cruise ships.