Estimation of influenza-associated mortality stratified by age, sex, and underlying cause of death

We have used proxies for disease incidence of the three influenza co-circulating subtypes (A/H3N2, A/H1N1 and B) that combine data on influenza-like illness consultations and respiratory specimen testing to estimate influenza-associated mortality in the US between 1997 and 2007, stratified by age, sex, and underlying cause of death. Elderly adults had the highest overall average flu-associated mortality rate, 140.23 (95% CI 117.20, 162.93) deaths per 100,000 people, while children under 18 had the lowest average mortality rate of 0.41(0.22, 0.58) per 100,000 people. Besides circulatory and respiratory causes, mortality underlying cancer, diabetes, renal disease and Alzheimer's had a significant contribution from influenza in several age groups. Influenza A/H1N1 had a more significant share of influenza-associated mortality in children compared to adults. For adults, within several age groups, influenza-associated mortality was somewhat higher in males than in females for several underlying causes (particularly circulatory causes). Of note, in males 50-64, our estimate 1.90 (1.17, 2.60) for the average annual rate per 100,000 persons for influenza-associated mortality underlying cancer is on par with the corresponding rate 1.82 (1.44, 2.21) of influenza-associated respiratory deaths. From the comparison of the non-influenza mortality baselines, we observed a disappearance of the “holiday season bump” in mortality in the period following the introduction of pneumococcal conjugate vaccine (PCV7). Age, sex, and underlying health conditions should be considered when planning influenza vaccination and treatment strategies.