A 7-year-old boy from rural Uttar Pradesh presents with a 10-day history of high-grade fever (39.5°C), abdominal pain, and constipation. On examination, he has hepatosplenomegaly and a faint rose-coloured rash on the trunk. Blood culture is pending. Complete blood count shows Hb 11.2 g/dL, WBC 6,500/μL with relative lymphocytosis, and platelets 120,000/μL. Widal test shows O antigen titre of 1:320 and H antigen titre of 1:160. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Enteric Fever ### Key Clinical Features **Key Point:** The constellation of prolonged fever (10 days), abdominal symptoms (pain + constipation), hepatosplenomegaly, and rose spots in a child from an endemic region is pathognomonic for enteric fever. ### Diagnostic Criteria Met | Feature | Finding | Significance | |---------|---------|---------------| | **Duration** | 10 days | Enteric fever typically peaks at 2–3 weeks; early presentation | | **Fever pattern** | High-grade (39.5°C) | Sustained fever, not intermittent | | **GI symptoms** | Constipation + abdominal pain | Classic in enteric fever (diarrhoea is less common in children) | | **Rash** | Rose spots (faint maculopapular) | Pathognomonic finding, seen in 5–30% of cases | | **Hepatosplenomegaly** | Present | Occurs in ~50% of enteric fever cases | | **Haematology** | Relative lymphocytosis, mild thrombocytopenia | Typical in enteric fever; WBC may be normal or low | | **Widal test** | O 1:320, H 1:160 | Diagnostic titre (≥1:160 in endemic areas); O > H suggests acute infection | ### Widal Test Interpretation in Enteric Fever **High-Yield:** In endemic regions like India, a single Widal titre ≥1:160 for O antigen is considered diagnostic. The O antigen rises first (days 6–8) and is more specific for acute infection; H antigen rises later and may persist from previous infection or vaccination. **Clinical Pearl:** Blood culture is the gold standard but takes 3–5 days; Widal test provides rapid presumptive diagnosis. In this case, the O antigen titre (1:320) exceeding H antigen (1:160) favours acute *Salmonella typhi* infection over past exposure. ### Pathophysiology 1. Ingestion of contaminated food/water → intestinal invasion 2. Penetration of Peyer's patches → bacteraemia (first week) 3. Seeding of reticuloendothelial system → hepatosplenomegaly 4. Rose spots: microabscesses in skin from septic emboli 5. Relative lymphocytosis: shift from neutrophilic response to lymphocytic predominance by week 2 ### Treatment Considerations **Key Point:** Third-generation cephalosporins (ceftriaxone 80 mg/kg/day) are first-line in children due to increasing fluoroquinolone resistance in India. Chloramphenicol is now rarely used due to toxicity. [cite:Park 26e Ch 5]