A farmer from Kerala presents with fever, jaundice, conjunctival suffusion, and oliguria after flooding. Leptospirosis is suspected. The GOLD STANDARD diagnostic test is:
- A Microscopic agglutination test (MAT) ✓
- B IgM ELISA for Leptospira
- C Weil-Felix reaction (OX-K titre)
- D Dark-field microscopy of blood in the first week
Correct answer: A. Microscopic agglutination test (MAT)
Explanation
The microscopic agglutination test (MAT) is the reference standard for leptospirosis serology, detecting serogroup-specific agglutinating antibodies using live or heat-killed Leptospira antigens. A titre of ≥1:100 in a single sample or a ≥4-fold rise between acute and convalescent sera confirms diagnosis. IgM ELISA (LEPTO dipstick) is more practical for field use but less sensitive in early disease. Dark-field microscopy has poor sensitivity (<40%) and is unreliable. Weil-Felix OX-K agglutination is used for scrub typhus, not leptospirosis.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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