With this study the investigators will try to assess the tolerability and measurability of the efficacy of non pharmaceutical measures to prevent seasonal influenza in individual households. Households with an identified index case of influenza will be randomised into one of three intervention arms: 1. group, where the household will receive general information about transmission of influenza virus and means to prevent it (Controls); 2. group, which will receive surgical masks and be asked to wear them whenever they are in close contact with the index case or other persons of the household that became ill during the observation period; 3. group, which will be given and asked to wear surgical masks as well as to execute intensified hand hygiene.

In addition to assessing the secondary attack rate as our primary outcome measure, the investigators will also try to evaluate compliance to those interventions by questionnaires.

Inclusion Criteria:

• influenza like illness symptoms
• positive rapid test for influenza
• inclusion within 48h of symptom onset
• inclusion of at least 3 members of a household (including index case)

Exclusion Criteria:

• severe illness
• other cases of similar symptoms within 14 days before onset of symptoms in index patient
• severe asthma or COPD
• pregnancy of index