The annual impact of seasonal influenza in the US: measuring disease burden and costs.

BACKGROUND Despite preventive efforts, influenza epidemics are responsible for substantial morbidity and mortality every year in the United States (US). Vaccination strategies to reduce disease burden have been implemented. However, no previous studies have systematically estimated the annual economic burden of influenza epidemics, an estimate necessary to guide policy makers effectively. OBJECTIVE We estimate age- and risk-specific disease burden, and medical and indirect costs attributable to annual influenza epidemics in the United States. METHODS Using a probabilistic model and publicly available epidemiological data we estimated the number of influenza-attributable cases leading to outpatient visits, hospitalization, and mortality, as well as time lost from work absenteeism or premature death. With data from health insurance claims and projections of either earnings or statistical life values, we then estimated healthcare resource utilization associated with influenza cases as were their medical and productivity (indirect) costs in $2003. RESULTS Based on 2003 US population, we estimated that annual influenza epidemics resulted in an average of 610,660 life-years lost (undiscounted), 3.1 million hospitalized days, and 31.4 million outpatient visits. Direct medical costs averaged $10.4 billion (95% confidence interval [C.I.], $4.1, $22.2) annually. Projected lost earnings due to illness and loss of life amounted to $16.3 billion (C.I., $8.7, $31.0) annually. The total economic burden of annual influenza epidemics using projected statistical life values amounted to $87.1 billion (C.I., $47.2, $149.5). CONCLUSIONS These results highlight the enormous annual burden of influenza in the US. While hospitalization costs are important contributors, lost productivity from missed work days and lost lives comprise the bulk of the economic burden of influenza.