A child with suspected enteric fever on day 8 of illness has blood cultures negative (treated earlier at peripheral facility). The most sensitive investigation at this stage of illness for confirming typhoid is:
- A Blood culture — 90% positive in first week, drops to 50% by second week
- B Widal test — positive from second week, but low specificity
- C Bone marrow culture — remains positive throughout and is most sensitive (>90%) even after antibiotic treatment ✓
- D Stool and urine culture — sensitivity increases from second week onward
Correct answer: C. Bone marrow culture — remains positive throughout and is most sensitive (>90%) even after antibiotic treatment
Explanation
Bone marrow culture has the highest sensitivity for typhoid fever (>90%) and, critically, remains positive even after several days of antibiotic treatment because intracellular macrophage organisms persist longer. Blood culture sensitivity drops from 80–90% in week 1 to 50% in week 2, and further in week 3. Widal test has poor specificity due to cross-reactions and endemic background positivity. Stool/urine cultures become positive in weeks 2–3 but are not as sensitive as bone marrow.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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