Legionella pneumophila

Legionella pneumophila is a bacterium that causes Legionnaire disease, a severe form of pneumonia. The disease was first identified in 1976 during an outbreak at an American Legion convention in Philadelphia, where 182 people contracted it, and 29 died.12

Symptoms typically begin with malaise and headache, followed by high fever, chills, cough, and shortness of breath. While healthy individuals can get sick, the elderly, debilitated, or those with suppressed immune systems are most at risk. The bacterium is often found in water systems, such as air-conditioning units or shower heads, and can spread through contaminated water droplets. It infects lung cells called macrophages, where it replicates before bursting them and spreading further. Treatment involves antibiotics, such as erythromycin. A milder form of Legionella infection, causing flu-like symptoms, is known as Pontiac fever.12