Legionnaires' Disease: What You Need to Know Now

Legionnaires' disease is a serious lung infection caused by Legionella bacteria. You may have heard about the 1976 outbreak at an American Legion convention — that’s where the name comes from. Today the bacteria still shows up in building water systems, hot tubs, and cooling towers. It can be mild for some people and life-threatening for others, so knowing the basics helps you act fast.

What to watch for

Symptoms usually start 2–10 days after exposure. Common signs are cough, high fever, shortness of breath, muscle aches, headache, and sometimes diarrhea or confusion. If you have flu-like symptoms that get worse instead of better, or you develop breathing trouble, get medical attention quickly. Older adults, people who smoke, and those with weakened immune systems are at higher risk for severe illness.

How doctors find and treat it

Doctors often use a urinary antigen test that detects Legionella pneumophila serogroup 1 — the most common type. They may also order a sputum culture or PCR to identify other strains. Chest X-rays can show pneumonia. Treatment is straightforward: antibiotics that reach the lungs, usually a macrolide like azithromycin or a fluoroquinolone such as levofloxacin. Mild cases can be treated at home if the doctor agrees, but severe cases need hospital care. Treatment length varies — commonly 5–10 days for uncomplicated cases and longer for people who are very ill or immunocompromised.

If you don’t improve on antibiotics or symptoms worsen, tell your provider. Early treatment lowers the risk of complications. Also mention any recent travel, hotel stays, or visits to places with large water systems — this helps public health find and stop outbreaks.

Legionella likes warm, stagnant water. It grows best between about 20°C and 50°C (68–122°F). That’s why cooling towers, poorly maintained hot tubs, decorative fountains, and complex plumbing in large buildings are common sources. Regular testing and maintenance of water systems cut the risk dramatically.

Prevention steps you can ask about or use: keep hot water hot (above 60°C at the heater, with safe delivery temperatures managed), keep cold water cold, flush rarely used taps, disinfect systems when needed, and ensure cooling towers and spas are properly cleaned. Building managers should follow local guidelines for Legionella control and document maintenance and testing.

If a cluster of cases appears, local health departments investigate. They trace exposures, test water sources, and recommend remediation. If you suspect an exposure at work or a public place, contact your local health authority — quick reporting helps stop outbreaks.

Got symptoms or worried about exposure? Call your healthcare provider, mention possible Legionella exposure, and get tested. If you manage a building, prioritize water system safety plans and routine checks. Small actions — like flushing unused taps and keeping temperatures controlled — prevent most problems.