Pandemic (H1N1) 2009 and Seasonal Influenza A (H3N2) in Children’s Hospital, Australia

outcomes of respiratory failure among hospitalized pneumonia patients with 2009 H1N1 infl uenza in Taiwan.sign of a robust infrastructure to monitor the safety of the pandemic A(H1N1) 2009 vaccination program in Taiwan. To the Editor: We read with interest the report by Carcione et al. of clinical features of pandemic infl uenza A (H1N1) 2009 and comparison of these with 2009 seasonal infl uenza infection in a population-based study from Western Australia (1). Here we share our experience of hospitalizations for infl uenza in a tertiary care children's hospital in Sydney, New South Wales, Australia, during the 3 peak infl uenza seasons of the last decade. During the 2009 Southern Hemisphere single infl uenza wave (June–September), we prospectively studied every child <15 years of age who was hospitalized with laboratory-confi rmed infl uenza (74% had proven pandemic [H1N1] 2009) in Children's Hospital at Westmead (CHW), Sydney, as part of a collaboration between the National Centre for Immunisation Research and Surveillance and the Australian Paediatric Surveillance Unit. The study was approved by the Human Research Ethics Committee at CHW and supported by the state (New South Wales) health department. Data from hospitalizations for seasonal infl uenza at CHW in 2003 and 2007 (previous peaks in the last decade) were analyzed by using our previous studies and medical records (2–4). To compare pneumonia rates, we used the same case defi nitions in 2007 and 2009 (radiologic changes consistent with pneumonia). Proportions were compared by using the χ 2 statistic. In 2009, the numbers of children with laboratory-confi rmed infl uenza admitted to the hospital and to the pediatric intensive care unit (PICU) at CHW (226 and 22, respectively) were nearly double those admitted in 2007 infl uenza-associated hospitalizations were for seasonal infl uenza A (H3N2) infection (Table). During the 2009 pandemic wave, of all children admitted with laboratory-confi rmed infl uenza, the proportion hospitalized with pandemic (H1N1) 2009 who were <6 months of age was similar to the proportion of children <6 months of age hospitalized with seasonal (H3N2) infl uenza in 2007 (21 [13%] of 167 and 21 [18%] of 119, respectively; p = 0.31). The proportions of those >5 years of age were signifi cantly higher (61 [37%] and 15 [13%]; p = 0.0001).