Legionnaires’ Disease Above Seasonal Expected Levels
Illinois Department of Public Health
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JB Pritzker, Governor |
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Sameer Vohra, MD, JD, MA, Director |
HEALTH ALERT
Increase in Legionnaires’ Disease Above Seasonal Expected Levels Summary and Action Items
Illinois is alerting providers to a nearly two-fold increase above expected baseline in reported cases of Legionnaires’ disease for June 2026.Providers should maintain a high index of suspicion for Legionnaires’ disease among patients with pneumonia and report Legionnaires' disease cases to their local health department.Providers are reminded to routinely evaluate Legionnaires’ disease in patients with healthcare associated exposures, especially among those living in residential healthcare facilities such as nursing homes.Healthcare facilities are reminded of the federal (CMS) requirement to have water management policies and procedures to reduce the risk of growth and spread of legionella and other opportunistic pathogens in building water systems.Reported Legionnaires’ disease incidence typically increases during warmer periods. Beginning in spring 2026, however, IDPH identified case counts exceeding expected baseline levels (based on 5-year medians). Notably, substantial deviations were observed in April and June, with increases of 92.6% and 81% above baseline, respectively. Additionally, by June 2026, IDPH had exceeded the number of presumptive healthcare-associated Legionella infection investigations over the prior year.Symptoms
Clinical features of Legionnaires’ disease include cough, fever, and radiographic pneumonia.
Legionella should be considered in the differential diagnosis for patients with the following:
< >Patients with severe pneumonia, in particular those requiring intensive careImmunocompromised patients with pneumoniaPatients with a travel history (patients who have traveled away from their home with an overnight stay within 10 days before the onset of illness) or hot tub usePatients at risk for Legionnaires’ disease with healthcare-associated pneumonia (pneumonia with onset > 48 hours after admission).Pontiac fever is a milder, self-limiting illness without pneumonia. Symptoms include fever, chills, myalgia, malaise, headaches, fatigue, nausea, and/or vomiting.
Transmission
Legionella is transmitted via inhalation of aerosolized water containing the bacteria. Less commonly, Legionella can also be transmitted via aspiration of drinking water. Legionella is not transmitted person-to-person.
Diagnosis
Signs and symptoms of Legionnaires’ disease are similar to pneumonia caused by other pathogens. The only way to confirm disease is through specific diagnostic testing. It is recommended that individuals with clinical findings compatible with and/or at high risk for Legionnaires’ disease have the following paired together:
Urine antigen test as part of the initial evaluation, performed as early as possible, ANDCulture of lower respiratory secretions (e.g., sputum, bronchoalveolar lavage), as is clinically appropriate/feasible.While the urine antigen gives a fast turnaround time to confirm Legionella infection, culture is important to identify species other than Legionella pneumophila serogroup 1. Further, IDPH’s public health laboratory can conduct genetic testing on isolates for cluster identification and to assist with source identification when environmental testing is performed. Additional information regarding testing can be found on CDC’s Laboratory Testing for Legionella page.
Treatment
Macrolides (such as azithromycin) and respiratory fluroquinolones (such as levofloxacin) are the preferred agents for treating Legionnaires’ disease. If Legionnaires’ disease is suspected, antibiotic treatment should not be withheld while waiting for urine antigen or culture results. Because Pontiac Fever is self-limiting, antimicrobial treatment is not recommended for patients with Pontiac Fever.
Prevention
The key to preventing Legionnaires’ disease is maintaining building water systems, including plumbing systems, cooling towers, and hot tubs, to reduce the risk of Legionella growth and spread. Water management programs identify hazardous conditions and take steps to minimize the growth and transmission of Legionella and other waterborne pathogens in building water systems and are federally required. In June 2017, CMS issued a memorandum requiring Medicare/Medicaid certified healthcare facilities to have water management policies and procedures to reduce the risk of growth and spread of Legionella and other opportunistic pathogens. Testing requirements for legionella bacteria are also codified in Illinois Long-Term Care Facilities, Part 300 Skilled Nursing and Intermediate Care Facilities Code. CDC provides a Toolkit for developing water management plans.
IDPH and LHD Response
Local health departments investigating cases of Legionnaires’ disease or Pontiac fever are asked to inquire about all potential exposures to aerosolized water and document those findings in I-NEDSS. Any epidemiological or geographical links should be reported to Savannah Ryals at [email protected] or phone 217-782-2016. IDPH staff work daily to identify single cases with presumptive health care exposures or clusters by exposure or geographical locations.
Contact
For questions or additional information about Legionella, please contact the IDPH Communicable Disease Control Section at 217-782-2016. Clinicians should contact their local health department to report cases.
Additional Resources
https://www.cdc.gov/legionella/index.html https://www.cdc.gov/legionella/downloads/fs-legionella-clinicians.pdf https://www.cdc.gov/control-legionella/php/toolkit/wmp-toolkit.html
Target Audience
Local Health Departments, Infectious Disease Physicians, Hospitals, Infection Preventionists, Health Care Providers, Long Term Care Facilities, Assisted Living Facilities, and Laboratories
Date Issued: July 23, 2026
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