Quantifying the burden of influenza: a prospective household contact study in France

Background: The actual impact of influenza epidemics cannot be accurately estimated from medical practice-based surveillance data. A prospective household contact study was performed in order to quantify the burden of influenza. Methods: The study took place in France between January and March 2000. A total of 947 households were recruited by 161 general practitioners (GP), from an “index-case” who consulted the GP for influenza-like illness. Virological specimens were collected for diagnosis of influenza and other respiratory pathogen infections. All household members were asked to complete a questionnaire, which included a 15-day follow-up, with details of clinical events, healthcare resources and work–sick leave. Results: Identified among household contacts were 395 influenza type A-positive index cases and 313 secondary cases. The median time to alleviation of major influenza symptoms was 8 days in index cases and 6 days in secondary cases. Forty-two percent of secondary cases did not consult while 15% consulted more than once. The mean number of treatments taken was respectively 3.7 and 2.2 in index and secondary cases. Work–sick leave was mainly associated with the severity of the illness. Conclusion: These results could help for quantifying the burden of influenza epidemics.