Burden of influenza-associated deaths in the Americas, 2002-2008

Background Influenza disease is a vaccine-preventable cause of morbidity and mortality. The Pan American Health Organization (PAHO) region has invested in influenza vaccines, but few estimates of influenza burden exist to justify these investments. We estimated influenza-associated deaths for 35 PAHO countries during 2002-2008. Methods Annually, PAHO countries report registered deaths. We used respiratory and circulatory (R&C) codes from seven countries with distinct influenza seasonality and high-quality mortality data to estimate influenza-associated mortality rates by age group (0-64, 65-74, and 75years) with a Serfling regression model or a negative binomial model. We calculated the percent of all R&C deaths attributable to influenza by age group in these countries (etiologic fraction) and applied it to the age-specific mortality in 13 countries with good mortality data but poorly defined seasonality. Lastly, we grouped the remaining 15 countries into WHO mortality strata and applied the age and mortality stratum-specific rate of influenza mortality calculated from the 20 countries. We summed each country's estimate to arrive at an average total annual number and rate of influenza deaths in the Americas. Results For the 35 PAHO countries, we estimated an annual mean influenza-associated mortality rate of 21/100000 among <65-year olds, 319/100000 among those 65-74years, and 1618/100000 among those 75years. We estimated that annually between 40880 and 160270 persons (mean, 85100) die of influenza illness in the PAHO region. Conclusion Influenza remains an important cause of mortality in the Americas.