What is the optimal clinical specimen for the recovery of Legionella pneumophila?

• A. Stool
• B. Blood
• C. Bronchial washings
• D. Nasopharyngeal swab

Answer: (C)

Legionella pneumophila is a fastidious organism that causes disease primarily in the lower respiratory tract, so the sample most likely to contain it is one taken from the lower airways. Bronchial washings collect material directly from the site of infection with minimal dilution from upper airway flora, increasing the chance of isolating the organism on culture. These specimens are typically plated on special media (like buffered charcoal yeast extract with iron and cysteine) and require longer incubation, so obtaining a sample rich in the organism enhances recovery.

Stool, blood, and nasopharyngeal swabs are less reliable for recovering Legionella because they either rarely contain the organism in detectable amounts or reflect colonization rather than true lower-respiratory infection.