A child receives 3 days of oral antibiotics before lumbar puncture for suspected bacterial meningitis. CSF now shows modest neutrophilic pleocytosis with near-normal glucose, and Gram stain and culture are negative. Which investigation is most useful to identify the causative agent?

• A Repeat CSF culture on chocolate agar
• B Serum procalcitonin level
• C Broad-range bacterial 16S rRNA gene PCR on CSF ✓
• D CSF adenosine deaminase activity

Explanation

Prior antibiotics rapidly sterilise CSF culture while leaving pleocytosis, so broad-range 16S rRNA PCR, which does not depend on viable organisms, is the test of choice in partially treated meningitis. Repeat culture remains negative once bacteria are killed, procalcitonin is a systemic inflammatory marker without species-level value, and CSF ADA supports tuberculosis rather than identifying pyogenic bacteria.

Reference: Nelson Textbook of Pediatrics, 22nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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