Clinical and etiological profile of children hospitalized with acute undifferentiated febrile illness in South-Eastern Rajasthan, India: a prospective observational study

Background: Etiological data on acute undifferentiated febrile illness (AUFI) in India come mainly from adults in humid, high-endemicity regions; pediatric data from semi-arid north-west India are sparse. We determined the etiology, laboratory profile, outcomes and laboratory discriminators in hospitalized children in south-eastern Rajasthan. Methods: Prospective observational study at a tertiary teaching hospital in Jhalawar, Rajasthan. Two hundred children aged 2 months–18 years with fever ≤7 days and no identifiable focus after baseline assessment underwent a standardized diagnostic panel. Proportions carry Wilson 95% confidence intervals (CIs). Sparse cell counts required Monte Carlo permutation testing (100 000 replicates) with Holm adjustment across 16 comparisons; threshold performance was assessed post hoc. Results: No etiology was identified in 105 children (52.5%, 95% CI 45.6–59.3). Scrub typhus predominated (33, 16.5%, CI 12.0–22.3; 34.7% of resolved diagnoses), then urinary tract infection (25, 12.5%), dengue (22, 11.0%), malaria (10, 5.0%) and enteric fever (5, 2.5%). Enrollment peaked in August–October (88, 44.0%; p<0.001). All laboratory parameters except creatinine differed by diagnosis (adjusted p≤0.002), as did length of stay, complications and defervescence time. Thresholds were specific but insensitive: hemoglobin <80 g/l for scrub typhus (specificity 97.0%, sensitivity 45.5%, likelihood ratio 15.2), platelets <100×10⁹/l for dengue (86.0%, 68.2%, 4.9). Complications affected 39 children (19.5%), intensive care 25 (12.5%); none died. Conclusions: Scrub typhus, not dengue or malaria, led identifiable causes and accounted for most transfusions. Empirical doxycycline warrants evaluation in post-monsoon fever. Routine thresholds modify suspicion but cannot replace specific testing; the unresolved half defines the gap molecular diagnostics must close.