Institute for Clinical and Translational Science

As causes of death, influenza and pneumonia are typically analyzed together. We quantify influenza’s contribution to the combined pneumonia and influenza mortality time series for the United States, 1959–2009. A key statistic is I/(P+I), the proportion of pneumonia and influenza mortality accounted for by influenza. Year-to-year, I/(P+I) is highly variable and shows long-term decline. Extreme values of I/(P+I) are associated with extreme P+I death rates and vice-versa, but I/(P+I) is a weak predictor of P+I mortality overall. Prominence of influenza in the medical news is associated with high I/(P+I). Influenza and pneumonia should be analyzed as a combined cause.