Microbial diagnostics · USMLE Step 1

A patient presents with fever, rash, and a history of tick exposure. What test is most appropriate for early detection of rickettsial infection?

  1. Serology for IgG antibodies
  2. Weil-Felix test
  3. PCR of blood
  4. Blood culture
Show answer and explanation

Correct answer: PCR of blood

PCR detects rickettsial DNA early in infection. Serology becomes positive only later in disease.

Difficulty: Medium Question 6 of 20

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