Which exposure is strongly associated with Legionella infection?

• A. Aerosolized water from air conditioning systems
• B. Contaminated dairy products
• C. Direct contact with infected animals
• D. Person-to-person respiratory spread

Answer: (A)

Exposure to Legionella is acquired primarily by inhaling aerosolized water that comes from man-made systems, especially air conditioning cooling towers, showers, hot tubs, and other warm-water sources. The bacteria grow in these water environments and are released in tiny droplets that can be breathed deep into the lungs, leading to infection. This route explains why buildings with complex water systems can be sources of outbreaks. In contrast, contaminated dairy products, direct contact with animals, or person-to-person respiratory spread are not typical routes for Legionella transmission, as the organism is not usually spread by ingestion, casual contact, or by passing from one person to another.