Legionella pneumophila infections are most often acquired from which source?

• A. Infections are acquired from environmental sources
• B. Metabolizes a number of carbohydrates
• C. Stains easily on the routine Gram stain
• D. Does not autofluoresce

Answer: (A)

Legionella infections are acquired from environmental water sources because the bacteria live in man-made water systems and infections occur when people inhale aerosols from contaminated water, such as showers, cooling towers, hot tubs, fountains, or plumbing systems. This environmental source explanation explains why human-to-human transmission is not typical and why outbreaks are linked to specific water environments.

Other statements miss the main point: while Legionella can be detected with specialized stains and fluorescent techniques, and it requires nonstandard culture media, these details describe detection and growth rather than how the infection is acquired. It’s not primarily about metabolizing carbohydrates in a way that defines transmission, and routine Gram stains do not reliably reveal Legionella.