American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the preferred test for detecting West Nile virus meningitis?

1. Antigen test in serum

2. Antibody detection in CSF

3. Blood culture

4. Rapid PCR in serum

The correct answer is: Antibody detection in CSF

The preferred test for detecting West Nile virus meningitis is the detection of antibodies in cerebrospinal fluid (CSF). This method is critical because it allows for the assessment of an immune response localized to the central nervous system (CNS), which is especially relevant in cases of viral meningitis. When the West Nile virus infects the CNS, the body mounts an immune response that results in the production of specific antibodies against the virus. Detecting these antibodies in the CSF indicates that the virus has successfully infiltrated the CNS, confirming a diagnosis of meningitis due to West Nile virus. Testing typically involves checking for immunoglobulin M (IgM) antibodies, as these are the first antibodies produced in response to an infection and are indicative of a recent or current infection. Other testing methods have limitations: serum antigen tests may detect viral components but do not confirm CNS involvement; blood cultures for West Nile virus are less reliable since the virus is often present in low abundance in the bloodstream; and rapid PCR tests on serum primarily indicate active infection but fail to provide the necessary information about CNS infection, which is integral for diagnosing meningitis specifically. Thus, antibody detection in CSF remains the gold standard for accurately diagnosing West Nile virus meningitis.