Characteristics and outcomes of pandemic 2009/H1N1 versus seasonal influenza in children with cancer

Background: Novel 2009/H1N1 influenza has significant impact on immunocompromised children with cancer; however, it is uncertain how it compares with seasonal influenza (SFlu) in this vulnerable population. We compared clinical characteristics and outcomes for these 2 infections in children with cancer and identified risk factors for progression to lower respiratory infection (LRI) and/or death. Methods: Influenza infections confirmed by positive viral culture and/or fluorescence antigen test between January 1998 and February 2010 were identified from microbiology databases at a comprehensive cancer center. Characteristics and outcomes were compared for the 2 groups. Kaplan-Meier survival curves and Cox proportional hazards model were generated to identify risk factors for LRI and/or death. Results: When compared with SFlu, 2009/H1N1 cases had significantly lower acute physiology and chronic health evaluation II score (median: 9 versus 14), fewer comorbidities (15% versus 46%), fewer hematopoietic stem-cell transplantation (5% versus 16%), more solid tumors (45% versus 16%), higher LRI at presentation (20% versus 4%), higher rates of antiviral therapy (90% versus 48%) and higher mortality (10% versus 0%). Male gender (hazard ratio [HR]: 8.4, 95% confidence interval [CI]: 1.08-65.2, P = 0.042), acute physiology and chronic health evaluation II score > 15 (HR: 3.29, 95% CI: 1.04-10.39, P = 0.027) and a 24-hour delay in initiation of antiviral treatment (HR: 1.12, 95% CI: 1.02-1.23, P = 0.015) were the most significant predictors of progression to LRI and mortality, regardless of virus strain. Conclusions: Significant differences between 2009/H1N1 and SFlu with respect to clinical presentation, management and associated outcomes were identified. Early diagnosis and prompt initiation of antiviral therapy may prevent serious complications of influenza in children with cancer.