In the Widal test for enteric fever, O antibodies and H antibodies have different clinical implications. Which interpretation is MOST CORRECT regarding Widal test results?

• A Rising O antibody titres are diagnostic of current active infection; H antibodies persist longer and may reflect past infection or vaccination ✓
• B H antibodies are always more significant than O antibodies in acute infection
• C A single Widal titre of O 1:80 is diagnostic of typhoid in all clinical settings
• D Widal test becomes positive in the first 2 days of fever and is most sensitive early in disease

Explanation

In the Widal test: O antibodies (somatic LPS antigens) appear earlier (end of first week), decline faster after recovery, and rising titres (4-fold rise in paired samples 2 weeks apart, or baseline ≥1:160 in non-endemic areas) are more indicative of current active infection. H antibodies (flagellar antigens) appear later, persist for months to years, and can reflect prior infection or TAB vaccination — hence high H titres with low O titres may indicate past infection or vaccination. A single O titre of 1:80 is considered suspicious in endemic areas (baseline titres may already be 1:40–1:80 in healthy people), and CLSI/standard guidelines require ≥1:160 O or paired samples. Widal test becomes positive only by the end of the first week (not 1–2 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.