Legionellosis

799 cases in 2024 — near the 5-year baseline of ~2,284.

What is it?

Legionellosis includes Legionnaires' disease (severe pneumonia) and Pontiac fever (milder illness) caused by Legionella bacteria. NYS had 799 cases in 2024. Outbreaks are often linked to building water systems — cooling towers, hot tubs, decorative fountains, and large building plumbing are common sources. Legionella is not spread from person-to-person.

How it spreads

People get infected by inhaling small water droplets (aerosols) or mist containing Legionella bacteria. Sources include cooling towers on rooftops, hot tubs and spas, decorative fountains, showers, and faucets in large buildings with stagnant warm water.

Symptoms

Legionnaires' disease: cough, shortness of breath, high fever (often 104°F or higher), muscle aches, and headache — a potentially fatal pneumonia. Pontiac fever: flu-like illness without pneumonia, resolving within 2–5 days without treatment.

Who is at risk?

Adults over 50, current or former smokers, people with chronic lung disease or weakened immune systems, and people with diabetes. Legionnaires' disease is the most common cause of waterborne disease outbreaks in the US.

What you can do

Based on NYSDOH annual communicable disease report. Threat level reflects 2024 case counts compared to the 5-year baseline.