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

Abstract

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 ≥ 75 years) 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 2·1/100,000 among <65-year olds, 31·9/100 000 among those 65-74 years, and 161·8/100,000 among those ≥ 75 years. We estimated that annually between 40,880 and 160,270 persons (mean, 85,100) die of influenza illness in the PAHO region.

Conclusion: Influenza remains an important cause of mortality in the Americas.

Keywords: Americas; influenza; model; mortality.

Figure 1

(A–G) Time series of monthly (A, B) or weekly (C–G) mortality rates coded as respiratory and circulatory causes from January 2002 through December 2009 (July 2002 through June 2010 for Mexico and United States). Blue line: observed mortality rates; red line: baseline rates predicted by a regression model; green line: predicted mortality rates. Periods highlighted in purple mark seasonal influenza epidemic periods. Y-axis: death rate (100 000 per person-years). (A) Argentina; (B) southern Brazil; (C) Chile; (D) Mexico; (E) Paraguay; (F) Uruguay; (G) United States.

Figure 2

Mean annual influenza mortality in Pan American Health Organization (PAHO) region, 2002–2008.