In the Widal test for enteric fever, which titre on a single serum sample is generally considered significant in an unimmunised patient from an endemic area?
- A O antibody titre ≥1:80 or a fourfold rise in paired sera ✓
- B O antibody titre ≥1:20
- C H antibody titre ≥1:160 alone
- D Any detectable O or H antibody titre
Correct answer: A. O antibody titre ≥1:80 or a fourfold rise in paired sera
Explanation
In unimmunised individuals from an endemic area, a single serum Widal O antibody titre of ≥1:80 (or ≥1:160 in some references) is considered significant, but a fourfold or greater rise in paired samples (acute + convalescent, 7–10 days apart) is the most reliable diagnostic criterion. H antibody titres alone are unreliable (they persist for years after infection or vaccination). The Widal test has significant limitations including cross-reactions with other enteric Gram-negatives; blood culture remains the gold standard for enteric fever.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.