The Illinois Department of Public Health (IDPH) is investigating four cases of Legionnaires’ disease in individuals who were at Advocate Christ Hospital in Oak Lawn, two of whom were patients within the past two months. The investigation is currently limited to this hospital. IDPH is working with the hospital to collect information and further investigate these cases, including an on-site visit by IDPH this week to test the facility’s water. The hospital is working with IDPH to strengthen its water management plan and implement multiple control measures. IDPH has recommended the facility provide information to potentially impacted patients and families about Legionella. Additionally, IDPH recommended that the facility conduct surveillance to identify other potential cases and to ensure appropriate testing and clinical management. 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.