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.