Performance of a syndromic system for influenza based on the activity of general practitioners, France

In France, as in other industrialized countries, syndromic surveillance systems for the early detection of illnesses have proliferated, but few validation studies on these systems performances exist. In Bordeaux, a south-western city in France, a system using a network of general practitioners house calls, such as SOS Médecins, provided local health data used to guide health service response, in particular in case of flu-like pandemic. We explored the capacity of SOS Médecins system to identify and follow influenza outbreaks using data from the Sentinel network, considered as being a gold standard for tracking seasonal influenza in France.

Data from SOS Médecins were analysed and compared with data from the Sentinel network. The sensitivity and specificity of SOS Médecins system were evaluated for different simulated thresholds.

A relationship between the number of visits for influenza from SOS Médecins and the number of influenza cases from the Sentinel network was observed; data from the two systems were highly correlated. We showed the capacity of SOS Médecins system to identify outbreaks with a sensitivity and specificity of 93%.

The sensitivity and specificity of SOS Médecins for early outbreak detection showed the value of these data in monitoring influenza activity.