Novel Influenza A(H1N1) Outbreak Among French Armed Forces in 2009: Results of Military Influenza Surveillance System

Objectives: An outbreak of novel A(H1N1) virus influenza, detected in Mexico in April 2009, spread worldwide in 9 weeks. The aim of this paper is to present the monitoring results of this influenza outbreak among French armed forces.

Study Design: The period of monitoring by the Military Influenza Surveillance System (MISS) was 9 months, from May 2009 to April 2010.

Methods: The main monitored events were acute respiratory infection (ARI), defined by oral temperature ≥38.5 °C and cough, and laboratory-confirmed influenza. Weekly incidence rates were calculated by relating cases to the number of servicepersons monitored.

Results: In continental France, the incidence of ARI increased from September 2009, with a weekly maxima of 401 cases per 100,000 in early December 2009 according to MISS. Estimations of the incidence of consultations which could be related to novel A(H1N1) influenza ranged from 48 to 57 cases per 100,000.

Conclusions: The trends observed by MISS are compatible with French national estimations. The incidence of consultations which could be related to A(H1N1) influenza at the peak of the epidemic (194 cases per 100,000) was much lower than the national estimate (1321 cases per 100,000). This may be due to servicepersons who consulted in civilian facilities and were not monitored. Other explanations are the healthy worker effect and the younger age of the military population.