Microbial diagnostics · USMLE Step 1

A clinician suspects Legionella pneumonia. Which diagnostic test is most specific and rapid?

  1. PCR of blood
  2. Culture on blood agar
  3. Urinary antigen test
  4. Sputum Gram stain
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Correct answer: Urinary antigen test

The urinary antigen test quickly detects L. pneumophila serogroup 1. It is widely used due to high specificity and rapid turnaround.

Difficulty: Medium Question 3 of 20

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