The survey in selected statistical residential districts will be performed via questionnaire regarding Influenza-like illness covering the months of January – April of the influenza epidemic 2016. This questionnaire will be distributed to 30’000 randomly selected households in those residential districts which were identified from the map analyses as “influenza hot spots” and some residential districts, in which influenza will not be as prevalent. Based on previous questionnaires at the same scale, we expect a 10% return rate. The questionnaire will cover the languages German, English, Italian, Turkish, Serbo-Croatian, and Albanian.