A leptospirosis patient's serum is tested by the Microscopic Agglutination Test (MAT). Serum at dilution 1:800 shows 50% agglutination of Leptospira interrogans serovar Icterohaemorrhagiae live antigen. What does this titre signify, and what is the first-line treatment?

• A Non-significant titre; no treatment needed
• B False positive; repeat with ELISA IgM
• C Borderline titre; wait for convalescent serum
• D Diagnostically significant titre; IV benzylpenicillin for severe disease ✓

Explanation

The Microscopic Agglutination Test (MAT) is the gold-standard serological test for leptospirosis. A titre of ≥1:100 in a single sample or fourfold rise in paired sera is considered significant; ≥1:400 is highly significant, and 1:800 with 50% agglutination is clearly diagnostic. The endpoint is defined as the highest dilution showing ≥50% agglutination of live leptospires compared to the antigen control. Treatment for severe leptospirosis (Weil's disease): IV benzylpenicillin 1.5 MU every 6 hours or IV ceftriaxone; mild disease: oral doxycycline 100 mg twice daily for 7 days.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.