This work aims to measure the effectiveness of face mask worn by a patient with flu to avoid transmission to other persons in the household.

Background. Non pharmaceutical interventions, and in particular the wearing of face masks, could play a role in controlling the transmission of influenza in the early stages of the epidemic. In the French pandemic plan, surgical masks are recommended in contagious patients in wards. The effectiveness of such masks in preventing transmission of influenza A virus is unknown. Our project aims to assess the preventive efficacy and tolerance of surgical mask.

The primary objective is to measure the decrease of the number of secondary cases of flu in households where the index case will wear a surgical mask during its period of infectiousness (5 days), compared to households where the index case will not be subject to this intervention. Secondary objectives are: (1) to study the feasibility and tolerance of wearing a mask continuously during the period of viral shedding; (2) virological description of infection spreading among household contacts based on virological collections.

Inclusion Criteria:

Patient seeking medical advice for:

• For symptoms less than 48 hours, combining fever> = 37.8 ° C and a cough,
• during the period of a seasonal influenza epidemic (as defined by the Sentinel network)
• Older than 5 years
• And living in a household size between 3 to 8..
• The patient is the first case in the household (index patient). The patient has a positive rapid influenza A test.
• Informed consent.
• Affiliation to the social security.

Exclusion Criteria:

• When concomitant influenza cases are known in other householders
• When the patient is suffering from asthma or COPD (ongoing treatment):
• Hospitalization.
• Treatment by a neuraminidase inhibitor.