Health impact of influenza in the United States.

Influenza infection is associated with significant morbidity and mortality. The purpose of this investigation was to describe the health effects of influenza in the US. Although a number of different data sources have been used to provide estimates of the health impact of influenza in the US, estimates provided in this article are primarily based upon the experiences reported in community-based studies performed in Houston, Texas, and Tecumseh, Michigan. Estimates of the annual average are provided for the following: (1) infection rate; (2) number of influenza-associated respiratory illnesses; (3) number of ill days with influenza; (4) number of bed and activity restriction days due to influenza illness; (5) physician visits; (6) hospitalisations and days hospitalised; and (7) mortality. Large differences were found between estimates from Houston and Tecumseh, and possible explanations for these are provided. However, all estimates find that influenza is an important cause of morbidity and mortality in the US.