The investigators hypothesize that sex, age, area of exposure and purpose of travel are associated with different travel-related infections. The investigators also hypothesize that certain infections will have long-term sequelae.

Health-data will be collected from travellers from Switzerland and Europe. The project starts with a pilot study for 50 travellers, followed by the recruiting of 10,000 travellers. The data collection will be via a mobile App (ITIT). The ITIT App will collect active data from travellers. The participants will download the App after signing an electronic consent form and completing a baseline questionnaire. Then the travellers will answer a short daily questionnaire about illness symptoms during travel. The ITIT App will also collect passive data (GPS localisation, environmental and weather data). The project will provide real-time data on travel-related infections and profile travel illness by age, sex and purpose of travel and also identify outbreaks.

International travel is growing exponentially. Globally, there will be a projected 1.8 billion traveller arrivals in 2030. Current surveillance of travellers' health is top-down (i.e., clinicians/laboratories report illness) and only a small proportion of illness events are captured. More data are needed on the types of infections acquired by different groups who have varying purposes of travel such as business/corporate travellers, those visiting friends and relatives (VFR), leisure/tourist travellers and mass gathering event (Hajj, Olympics, World Cup) attendees. More data are needed to profile infections in travellers according to age and sex as men and women have different infection susceptibilities. Infectious diseases, in particular the spread of malaria and "arboviral infections",(i.e. viruses such as dengue) pose major threats with changing epidemiology influenced by climate, environmental factors and human mobility. The extent and impact of these infections on travellers' health and their long-term sequelae have scarcely been evaluated. The collected data will allow the profiling of infections in travellers according to purpose of travel and according to age and sex. Men and women have different infection susceptibilities but there is just one study on this theme in the context of travel medicine Infectious diseases, in particular the spread of malaria and "arboviral infections", i.e. viruses such as dengue, chikungunya and Zika pose major threats with changing areas of transmission influenced by climate and mobility. Although airline statistics are available on traveller numbers, the volume of ill, returning, possibly viremic travellers entering areas, where susceptible vectors exist has never been quantified. The situation of a twin presence of viremic travellers and competent Aedes vectors may lead to the onward transmission of arboviral infections. The ITIT project, evaluating in-travel and post-travel illness profiles, coupled with geo-location and meteorological data, will yield the granular data needed for personalized travel medicine. This is important given the heterogenicity and increasing volume of global travellers. The project has the support of the World Health Organization (WHO). Since the data will be collected anonymously via a questionnaire on the designed mobile App and the study is non-interventional, the risk category for this project is minimal (A).

Inclusion Criteria:

1. travellers who cross international borders
2. adults (over 18 years old)
3. those traveling for more than 2 days and less than 8 weeks

Exclusion Criteria:

1. Non travellers (not crossing international borders)
2. Minors (under 18 years old)
3. those traveling for less than 2 days and longer than 8 weeks

International travellers who cross international borders and are traveling for varying purposes such as business/corporate travellers, those visiting friends and relatives (VFR), leisure/tourist travellers and mass gathering events (Hajj, Olympics, World Cup) attendees.