Medical Advisory: Legionellosis - Heightened Awareness

Issued by: Dr. Azim Kasmani, MD, MSc, FRCPC, Medical Officer of Health and Commissioner
Date: May 19, 2026

The Ontario Ministry of Health is actively monitoring two concurrent legionellosis clusters, located in Hamilton and Toronto.

Health care providers are asked to maintain a high index of suspicion for legionellosis in patients presenting with pneumonia, particularly in adults over 60 years of age.

Testing

Best practice for laboratory diagnosis of legionellosis includes the collection of both lower respiratory specimens (for PCR and culture) and urine (for antigen testing). While the Urinary Antigen Test (UAT) is commonly used, it only detects L. pneumophila serogroup 1 and does not detect infection caused by non-serogroup 1 or allow for sequencing. Submitting a lower respiratory specimen (culture) is critical, as a clinical culture isolate is required to make a genetic linkage to an environmental culture during source investigations

For hospitalized patients specimens should be collected during the acute phase of illness, as close to admission as possible. Antibiotic treatment should not be delayed to collect specimens.

Specimens should be sent in a sterile container and include symptoms and onset date on the Public Health Ontario lab General Test Requisition Form.

Notification

Legionellosis must be reported to Niagara Region Public Health by the next working day:

Monday to Friday, 8:30 a.m. to 4:30 p.m.: 905-688-8248 ext. 7330 (toll-free: 1-888-505-6074)
After hours: 905-984-3690

Infection Prevention and Control (IPAC)

To increase awareness about environmental cleaning and practical approaches to help better understand and control legionellosis in health care settings, see presentations by Public Health Ontario:

More Information

Contact the Infectious Disease Program at 905-688-8248 ext. 7330