RESUMEN
<p><b>INTRODUCTION</b>The pandemic caused by the H1N1 influenza virus in 2009 resulted in extensive morbidity and mortality worldwide. As the virus was a novel virus, there was limited data available on the clinical effects of the virus on children in Malaysia. Herein, we describe the clinical characteristics of children hospitalised with H1N1 influenza in a tertiary care centre; we also attempted to identify the risk factors associated with disease severity.</p><p><b>METHODS</b>In this retrospective study, we compared the characteristics of the children who were admitted into the University of Malaya Medical Centre, Malaysia, for H1N1 influenza during the pandemic with those who were admitted for seasonal influenza in 2002-2007.</p><p><b>RESULTS</b>Among the 77 children (aged ≤ 12 years) admitted to the centre due to H1N1 influenza from 1 July 2009-30 June 2010, nearly 60% were aged < 6 years and 40.3% had an underlying medical condition. The top three underlying medical conditions were bronchial asthma (14.3%), cardiac disease (10.4%) and neurological disorder (11.7%). The risk factors for severe disease were age < 2 years, underlying bronchial asthma and chronic lung disease. The three patients who died had a comorbid medical condition. The underlying cause of the deaths was acute respiratory distress syndrome or shock.</p><p><b>CONCLUSION</b>The clinical presentation of the children infected with the pandemic (H1N1) 2009 influenza virus did not differ significantly from that of children infected with seasonal influenza. However, there were more complaints of fever, cough and vomiting in the former group.</p>