To collect data to elaborate hypotheses regarding the source of the outbreak. 

Food and water  

Questionnaire 1. Generating a hypothesis.
In: Strengthening surveillance of and response to foodborne diseases: a practical manual. Stage 1: investigating foodborne disease outbreaks. (Geneva: World Health Organization 2017) 

Questionnaire 2. Testing hypothesis.
In: Strengthening surveillance of and response to foodborne diseases: a practical manual. Stage 1: investigating foodborne disease outbreaks. (Geneva: World Health Organization 2017)