In Widal test interpretation for enteric fever, a single convalescent titer of anti-O ≥1:160 is significant. Which of the following statements about Widal test limitations is CORRECT?
- A Previous typhoid vaccination or prior infection can cause elevated baseline titers ('recall reaction'), making single-sample interpretation unreliable in endemic areas ✓
- B Anti-H agglutinins are more specific for active infection than anti-O agglutinins as H antigens are not shared between Salmonella serotypes
- C The Widal test becomes positive in the first 48 hours of illness, allowing early diagnosis during the bacteremic phase
- D Widal test is performed on CSF to diagnose typhoid meningitis as blood cultures are always negative in this complication
Explanation
The major limitation of the Widal test is the lack of specificity in endemic regions. Previous typhoid vaccination (TAB vaccine) or prior natural infection can leave residual anti-O and anti-H titers that may reach or exceed the diagnostic threshold — this is called a 'anamnestic' or 'recall reaction.' In such individuals, a single titer is uninterpretable without paired acute-convalescent samples (4-fold rise is needed for definitive diagnosis). Anti-H titers are actually LESS specific than anti-O because H antigens are shared between Salmonella serotypes and other Enterobacteriaceae (causing cross-reactions). Widal antibodies appear in the 2nd week of illness, not in the first 48 hours. Blood culture (not Widal) is the gold standard for bacteremic typhoid.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.