Legionella pneumonia is typically acquired by

• A. Inhalation of aerosols from contaminated water or soil
• B. Direct person-to-person transmission
• C. Ingestion of contaminated water
• D. Inhalation of airborne spores from soil

Answer: (A)

Legionella pneumonia is acquired when people inhale aerosols that contain the bacteria. Legionella grows in engineered water systems—think hot water tanks, showers, cooling towers, and other sources that create fine water droplets. When these contaminated aerosols are inhaled, the bacteria reach the lungs and can cause pneumonia. It isn’t spread from person to person, and it isn’t acquired by simply drinking contaminated water. The idea of inhaling airborne spores from soil isn’t the typical route for Legionella, since transmission occurs via water-derived aerosols. So the key mechanism is inhalation of aerosols from contaminated water or related sources.