Clinical predictors of influenza in children

Background: It is difficult to diagnose influenza infection on clinical grounds alone. Available rapid diagnostic tests have limited sensitivities. Objective: To develop a prediction model that identifies children likely to have influenza infection. Design: Prospective study. Setting: Emergency department of a children's hospital Patients: All patients with a febrile respiratory illness during the influenza season of winter 2002 were eligible. A prospective sample of 128 children who were suspected of having influenza infection based on predetermined criteria was enrolled. Each patient received a nasal wash for viral culture. Main Outcome Measure: Clinical features that are most predictive of influenza infection in children. Results: The mean+/-SD age of patients was 6.2+/-5.2 years; 50% were boys. Viral isolates included the following: influenza A, 45 patients (35%); influenza B, 13 (10%); other viruses, 10 (8%); negative results, 60 (47%). Demographic and clinical findings were not significantly different between the influenza A and influenza B groups. Cough (P=.003), headache (P=.04), and pharyngitis (P=.04) were independently associated with influenza infection. This triad used as a prediction model for influenza infection had a sensitivity of 80% (95% confidence interval [CI], 69%-91%); specificity, 78% (95% CI, 67%-89%); and likelihood ratio for a positive viral culture for influenza, 3.7 (95% CI, 2.3-6.3). The posttest probability of this clinical definition is 77% (95% CI, 63%-91%). Conclusion: The triad of cough, headache, and pharyngitis is a predictor of influenza infection in children.