By using this new technology, an extensive collection of data (prospective collection of individual travel behaviour and experienced health events, mapping the travel itinerary via global positioning system (GPS), linking to publicly available local weather data and data on disease endemicity) can be combined and an unprecedented abundance of information on travel behaviour and experienced risks can be obtained. These data will allow a much better understanding of travel risk profiles using cluster analysis. By simultaneously recording health outcomes, the relationship between travel risk profiles and health events can be assessed. In this study, the investigators will address several major shortcomings in travel health in tropical and subtropical destinations by improving the understanding of poorly assessed and potentially underestimated health threats (e.g. risk of accidents and injury, mental health disorders), and travel risks specific to elderly travellers and travellers with chronic conditions. These findings will directly feed back into individual travel advice given by practitioners in Switzerland and finally world-wide.