Estimates of mortality attributable to influenza and RSV in the United States during 1997–2009 by influenza type or subtype, age, cause of death, and risk status

BACKGROUND: Influenza and respiratory syncytial virus (RSV) cause substantial mortality from respiratory and other causes in the USA, especially among people aged 65 and older. OBJECTIVES: We estimated the influenza-attributable mortality and RSV-attributable mortality in the USA, stratified by age and risk status, using outcome definitions with different sensitivity and specificity. METHODS: Influenza- and RSV-associated mortality was assessed from October 1997-March 2009 using multiple linear regression modeling on data obtained from designated government repositories. RESULTS: The main outcomes and measures included mortality outcome definitions-pneumonia and influenza, respiratory broad, and cardiorespiratory disease. A seasonal average of 10,682 (2287-16,363), 19,100 (4862-29,245), and 28,169 (6797-42,316) deaths was attributed to influenza for pneumonia and influenza, respiratory broad, and cardiorespiratory outcome definitions, respectively. Corresponding values for RSV were 6211 (4584-8169), 11,300 (8546-14,244), and 17,199 (13,384-21,891), respectively. A/H3N2 accounted for seasonal average of 71% influenza-attributable deaths; influenza B accounted for most (51-95%) deaths during four seasons. Approximately 70% influenza-attributable deaths occurred in individuals ≥75 years, with increasing mortality for influenza A/H3N2 and B, but not A/H1N1. In children aged 0-4 years, an average of 97 deaths was attributed to influenza (A/H3N2 = 49, B = 33, A/H1N1 = 15) and 165 to respiratory broad outcome definition (RSV). Influenza-attributable mortality was 2.94-fold higher in high-risk individuals. CONCLUSIONS: Influenza-attributable mortality was highest in older and high-risk individuals and mortality in children was higher than reported in passive Centers for Disease Control and Prevention surveillance. Influenza B-attributable mortality was higher than A in four of 12 seasons. Our estimates represent an updated assessment of influenza-attributable mortality in the USA.