Which specimen provides the best yield for recovery of Legionella pneumophila?

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

Answer: (C)

The specimen from the lower respiratory tract provides the highest chance of recovering Legionella pneumophila because the bacteria reside and multiply in the alveolar spaces during pneumonia. Bronchial washings sample directly from the infected airways, yielding a higher bacterial load and a more representative specimen for culture on selective media (such as cysteine-containing media) or for other detection methods. In contrast, stool and nasopharyngeal swabs often contain little to no organism and have more competing microorganisms, and blood cultures are rarely positive for Legionella. For these reasons, bronchial washings offer the best yield for recovery.