Estimates From a National Prospective Survey of Household Contacts in France

Background: The burden of influenza among ambula- tory patients is still relatively unknown, although this knowledge is crucial for evaluating strategies against in- fluenza. We estimated the impact of influenza in terms of uncomplicated morbidity and its consequences on health care utilization and lost workdays. of them visited a physician at least once (consulting sec- ondary cases). The median duration of illness was 8 days (95% confidence interval (CI), 7-8 days) in index cases, 7 days (95% CI, 7-8 days) in consulting secondary cases, and 4 days (95% CI, 3-5 days) in nonconsulting second- ary cases (P.001); the median duration of treatment in these groups was 8 days (95% CI, 8-9 days), 8 days (95% CI, 7-10 days), and 5 days (95% CI, 4-6 days), respec- tively (P.001); and their mean±SD number of lost work- days was 4.0±2.8, 2.9±2.5, and 0.3±0.6, respectively, in working adults (P.001). Conclusions: These results confirm the substantial bur- den of illness of influenza. The results should be useful for evaluating the cost-effectiveness of strategies against influenza.