How is Q fever usually diagnosed?

How is Q fever usually diagnosed?

• A. Culture of Coxiella burnetii from blood
• B. Serology testing for IgG against phase I and II antigens
• C. PCR of throat swab
• D. Urinalysis

Answer: (B)

Diagnosing Q fever relies on detecting the body's antibody response to Coxiella burnetii, specifically IgG against phase I and phase II antigens. This organism is difficult to culture safely and often doesn’t yield reliable results from routine cultures, so serology provides the practical and accurate way to confirm infection. In acute Q fever, antibodies to phase II antigens rise first, and a high IgG titer against phase II (often with or without IgM) supports acute infection. Chronic Q fever shows elevated antibodies to phase I antigens, reflecting a different clinical course. Using paired sera to demonstrate a rising titer helps confirm recent infection. While PCR can identify bacterial DNA and may be helpful early in illness, serology is the standard, widely available method used to diagnose Q fever. Culturing Coxiella from blood is not routinely done due to biosafety concerns and low yield, and tests on throat swabs or routine urinalysis are not relevant for this diagnosis.

Diagnosing Q fever relies on detecting the body's antibody response to Coxiella burnetii, specifically IgG against phase I and phase II antigens. This organism is difficult to culture safely and often doesn’t yield reliable results from routine cultures, so serology provides the practical and accurate way to confirm infection.

In acute Q fever, antibodies to phase II antigens rise first, and a high IgG titer against phase II (often with or without IgM) supports acute infection. Chronic Q fever shows elevated antibodies to phase I antigens, reflecting a different clinical course. Using paired sera to demonstrate a rising titer helps confirm recent infection.

While PCR can identify bacterial DNA and may be helpful early in illness, serology is the standard, widely available method used to diagnose Q fever. Culturing Coxiella from blood is not routinely done due to biosafety concerns and low yield, and tests on throat swabs or routine urinalysis are not relevant for this diagnosis.