1000 clients traveling to Thailand, China, India, Brazil, Peru or Tanzania will be recruited from the Travel Clinics in Zurich and Basel and through advertising at local travel agents and the universities of ETH and UZH from September 2017 until February 2019. After completing an intake at the clinic, participants will be given the option to use their own Smartphone for data collection, or to use a phone owned by the UZH-EBPI during travel. Participants will use a data collection app for questionnaire responses during and after travel including: a daily questionnaire on travel behaviors, daily symptoms questionnaire, and localization tracking, showing the participants' travel path and locations.