Context: Data are limited on rates of influenza-associated hospitalizations and deaths among adults younger than 65 years.
Objective: To quantify serious morbidity and mortality from influenza for women younger than 65 years with and without certain chronic medical conditions, including human immunodeficiency virus infection.
Design: Retrospective cohort study.
Setting and population: Women aged 15 to 64 years enrolled in the Tennessee Medicaid program from 1974 to 1993.
Main outcome measure: All hospitalizations for and deaths from pneumonia, influenza, and other selected acute cardiopulmonary conditions for women with and without selected chronic medical conditions during 19 consecutive years. Influenza-attributable risk was calculated by subtracting event rates during peri-influenza season (November through April of each year when influenza virus was not circulating) from adjusted rates during influenza season (November through April when influenza virus was circulating).
Results: During the 19 years of the study, we identified 53607 acute cardiopulmonary hospitalizations and deaths. Rates of such events were consistently higher during influenza seasons than peri-influenza seasons. Among high-risk women, the estimated annual excess was 23 hospitalizations and deaths per 10000 women aged 15 to 44 years and 58 such events per 10000 women aged 45 to 64 years. The estimated annual excess mortality due to influenza was 2 deaths per 10000 high-risk women for both age groups combined. Among women with no identified high-risk conditions, estimated annual excess hospitalizations and deaths were 4 and 6 per 10000 women aged 15 to 44 and 45 to 64 years, respectively.
Conclusions: Women younger than 65 years with certain chronic medical conditions experience substantial morbidity and mortality from acute cardiopulmonary events during influenza season. More effective targeting of these populations for annual influenza immunization is warranted.