Legionella pneumophila infections are most often acquired from which sources?

• A. Infections are most often acquired from environmental sources.
• B. Metabolizes a number of carbohydrates
• C. Stains easily as gram-negative bacilli
• D. Does not autofluoresce

Answer: (A)

Legionella infections are acquired primarily through inhalation of aerosolized water containing the organism. It thrives in man-made water systems—hot water tanks, cooling towers, showers, decorative fountains, and humidifiers—where people can breathe in tiny droplets that carry the bacteria. Transmission is not person-to-person, nor is it typically from drinking water. That makes environmental sources the most common route of acquisition.

Laboratory or staining characteristics aren’t about how people get infected. Legionella can be difficult to see with standard Gram staining and often requires special stains or culture methods, and detection may involve immunofluorescence, but these points pertain to identification, not acquisition. Similarly, autofluorescence is a lab property used for detection, not a transmission route.