Clinical epidemiology and predictors of outcome in children hospitalised with influenza A(H1N1)pdm09 in 2009: a prospective national study

BACKGROUND There are few large-scale, prospective studies of influenza A(H1N1)pdm09 in children that identify predictors of adverse outcomes. OBJECTIVES We aimed to examine clinical epidemiology and predictors for adverse outcomes in children hospitalised with influenza A(H1N1)pdm09 in Australia. METHODS Active hospital surveillance in six tertiary paediatric referral centres (June-September, 2009). All children aged <15 years admitted with laboratory-confirmed influenza A(H1N1)pdm09 were studied. RESULTS Of 601 children admitted with laboratory-confirmed influenza, 506 (84·2%) had influenza A(H1N1)pdm09. Half (51·0%) of children with influenza A(H1N1)pdm09 were previously healthy. Hospital stay was longer in children with pre-existing condition (mean 6·9 versus 4·9 days; P = 0·02) as was paediatric intensive care unit (PICU) stay (7·0 versus 2·3 days; P = 0·005). Rapid diagnosis decreased both antibiotic use and length of hospital and PICU stay. Fifty (9·9%) children were admitted to a PICU, 30 (5·9%) required mechanical ventilation and 5 (0·9%) died. Laboratory-proven bacterial co-infection and chronic lung disease were significant independent predictors of PICU admission (OR 6·89, 95% CI 3·15-15·06 and OR 3·58, 95% CI 1·41-9·07, respectively) and requirement for ventilation (OR 5·61, 95% CI 2·2-14·28 and OR 5·18, 95% CI 1·8-14·86, respectively). Chronic neurological disease was a predictor of admission to PICU (OR 2·30, 95% CI 1·14-4·61). CONCLUSIONS During the 2009 pandemic, influenza was a major cause of hospitalisation in tertiary paediatric hospitals. Co-infection and underlying chronic disease increased risk of PICU admission and/or ventilation. Half the children admitted were previously healthy, supporting a role for universal influenza vaccination in children.