In typhoid fever, Widal test interpretation requires knowledge of background titers in endemic areas. A single Widal test showing O titer of 1:160 and H titer of 1:80 in an unimmunised patient from a non-endemic area is:

• A Suggestive of active typhoid — elevated O titer (1:160) with lower H titer indicates recent somatic antigen stimulation ✓
• B Diagnostic of active typhoid fever; both O and H titers are equally significant
• C Non-diagnostic — only paired sera showing fourfold rise is valid; single test has no value
• D Consistent with past typhoid vaccination — H titer is more significant than O titer for active disease

Explanation

In Widal test interpretation, O (somatic LPS) antibodies appear earlier and indicate active or recent infection; H (flagellar) antibodies appear later, persist longer, and may indicate past infection or vaccination. In an unimmunised patient from a non-endemic area, an O titer ≥1:80–1:160 is considered presumptive evidence of active typhoid. The pattern of high O titer (1:160) with relatively lower H titer in a single specimen in a non-endemic area strongly suggests acute typhoid. Paired sera (fourfold rise) is confirmatory but impractical in emergency settings. Vaccination raises H titers more than O titers.

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

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Written and medically reviewed by the StethoPrep medical team.