ICYMI: From the Wisconsin Division of Public Health: Legionnaires’ Disease Advisory – Please read

It’s that time of year again when Legionnaires’ diseases cases begin to increase in Wisconsin. During the warmer summer months, people are more likely to be exposed to Legionella bacteria through aerosolized water droplets. Water droplets can aerosolize from showers and other fixtures, cooling towers (parts of certain large air conditioning systems), decorative fountains, hot tubs, and other human-made water systems.

Wisconsin providers reported 210 laboratory-confirmed cases of Legionnaires’ disease in 2025, compared to a 5-year average of 217 reported laboratory-confirmed cases per year. Legionnaires’ disease incidence in Wisconsin was approximately 3.7 cases per 100,000 residents per year from 2021–2025, approximately 50% higher than the 2021 national average based on recent CDC surveillance data.

We need your help in diagnosing and reporting cases of Legionnaires’ disease to promptly identify sources of Legionella exposure to prevent further infections.

Legionnaires’ disease testing

There are a number of considerations when determining who should be tested for Legionnaires’ disease. Questions to consider may include:

• Does the patient have pneumonia?
• Have they traveled recently?
• Have they had a recent potential exposure?

You can find a list of situations in which you should test your patients for Legionnaires’ disease by visiting the Department of Health Services (DHS) legionellosis webpage.

When testing for Legionnaires’ disease, both a Legionella culture and a urine antigen test should be ordered. A Legionella culture requires collection of sputum or other lower respiratory specimens. Sputum or other lower respiratory specimens should also be used to perform Legionella PCR testing. Legionella PCR is often more sensitive than Legionella urine antigen tests and Legionella culture for detecting cases of Legionnaires’ disease.

Testing best practices

• Make sure you’re not missing some species and serogroups. Urine antigen tests will only detect Legionella pneumophila serogroup 1, resulting in a missed opportunity to diagnose approximately 20% of all Legionnaires’ disease cases if not paired with either a Legionella culture or Legionella PCR test.
  • The Wisconsin State Laboratory of Hygiene (WSLH) offers fee for service Legionella culture and Legionella PCR testing for diagnostic purposes. WSLH’s Legionella PCR test uses multiple DNA targets to identify and differentiate infections caused by Legionella pneumophila serogroup 1, other serogroups of Legionella pneumophila, as well as other species of Legionella.
• Don’t throw out sputum or other lower respiratory specimens. Laboratories should not discard sputum or other lower respiratory specimens after a routine sputum culture for pneumonia. A Legionella culture should be ordered even if there is less than 5mL of specimen left and the patient has already tested positive using a Legionella urine antigen test or Legionella PCR test.
  • Additionally, laboratories should not reject lower respiratory specimens for Legionella culture based on lack of white blood cells in the sample or contamination with other bacteria in the sample. Legionella can often be recovered on selective media.
• Send a sputum sample to WSLH for all Legionella urine antigen or PCR positive cases of Legionnaires’ disease. A Legionella culture is important for surveillance purposes and outbreak investigations. WSLH offers fee-exempt Legionella culture when it is ordered for public health surveillance purposes. Legionella will not grow on standard media used for routine respiratory cultures. A Legionella culture must be specifically ordered. See instructions for laboratories on how to ship specimens to WSLH.
  • DHS approval is not needed for Legionella culture testing for patients with a positive Legionella urine antigen test or a positive Legionella PCR test. Laboratories should indicate that the testing is being performed for surveillance purposes on the requisition form.
  • Urine and nasopharyngeal swabs are not validated specimens for Legionella culture testing and will be rejected if sent.

Help us find the source of exposure. Isolates obtained from Legionella culture are very helpful in comparing patients to Legionella isolates from environmental samples. This comparison is only possible if sputum or lower respiratory specimens are collected, Legionella culture is ordered, and isolates are sent to WSLH.

Report cases as soon possible

Legionnaires’ disease is a Wisconsin Disease Surveillance Category II disease. Cases should be reported to the patient’s local public health department electronically through the Wisconsin Electronic Disease Surveillance System (WEDSS), by mail, by fax using an Acute and Communicable Disease Case Report, F-44151, or by other means within 72 hours upon recognition.

For more information see the Case Reporting and Investigation Protocol (previously called EpiNet). Public health will investigate reported cases of Legionnaires’ disease in accordance with the Wisconsin Legionellosis Case Investigation Protocol.

Health care facility managers: You can prevent healthcare-associated Legionnaires’ disease!

Legionnaires’ disease can be prevented by minimizing growth of Legionella bacteria in building water systems. One of the most effective ways to prevent healthcare-associated Legionnaires’ disease is to implement a water management program that is compliant with the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Standard 188, ASHRAE Guideline 12, and ASHRAE Standard 514.

The Centers for Medicare & Medicaid Services requires hospitals and long-term care facilities to implement a water management program that meets industry standard. Some other settings are also recommended to develop a water management program. Use this short worksheet to assess the need for a water management program in your facility.

The Centers for Disease Control and Prevention (CDC) offers a toolkit to assist with developing a water management program. For facilities that currently have a water management program, consider using the Council of State and Territorial Epidemiologists’ (CSTE) Water Management Program Evaluation Tool to perform a gap analysis on the current program and identify potential areas for improvement. CSTE also has remediation resources to help facilities when developing contingency responses as a part of the water management program.

Find additional materials such as toolkits, trainings, templates, fact sheets, FAQs, and special considerations on Legionnaires’ disease for facility managers on the DHS legionellosis webpage.

Resources

• DHS Legionellosis webpage: Detailed recommendations for health care providers, laboratorians, local and Tribal public health departments, and health care facility managers.
• Diagnosing Legionnaires’ Disease: Best Practices, P-02433: One-page factsheet on diagnostic best practices.
• Resources to help health care facility managers implement an effective water management program to prevent cases of healthcare-associated Legionnaires’ disease:
  • Toolkit: Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings (CDC)
  • Water Management Program Evaluation Tool (CSTE)
  • Healthcare Facility Water Management Program Checklist (CDC)
  • Water Infection Control Risk Assessment (CDC)
  • Legionella Remediation Options for Building Water Systems (CSTE)
• Information on Legionella testing available at WSLH, including validated specimen types, rejection criteria, and packaging requirements:
  • Legionella RT-PCR
  • Legionella Clinical Culture

Thank you so much for your help preventing, diagnosing, and reporting Legionnaires’ disease.