1 This application describes the proposal from GeoSentinel, a global surveillance network 2 operating under the auspices of the International Society of Travel Medicine, in response to the 3 CDC notice of funding opportunity RFA-CK-21-002. GeoSentinel has operated continuously 4 since 1996 by virtue of a series of cooperative agreements with the CDC and other funding 5 sources. The network currently consists of 68 sites in 28 countries on 6 continents, as well as 6 191 affiliate sites. Our primary sites are high volume tropical and travel medicine clinics, and are 7 directed by practitioners recognized for their clinical expertise and academic experience. These 8 clinics all have routine access to the full spectrum of modern diagnostic resources, allowing 9 them to establish diagnoses for ill returning travellers and migrants using the highest standards 10 of accuracy. 11 GeoSentinel has been primarily a surveillance network since its inception, although we have 12 gradually increased our research capacity. We have always focused on using travelers and 13 migrants as sentinels for the detection of emerging infections and outbreaks around the world, 14 which is exceptionally valuable to supplement information from regions where local surveillance 15 may be suboptimal. In this proposal, we propose a shift towards using our unique platform 16 primarily to answer more research oriented questions in the field. We will continue our highly 17 successful surveillance system, with each of our sites continuing to enter clinical, travel, and 18 diagnostic data on all eligible ill returning travellers, continuing to build the database which 19 produced many analyses greatly improving our understanding of the epidemiology of imported 20 infection, and has provided sentinel event notifications. Our more recent “enhanced 21 surveillance” strategy involves collected more detailed data on selected travel populations over 22 a defined time period to answer high priority, focused questions. This strategy now includes 23 research objectives, studied using patient questionnaires, standardised follow-up and outcome 24 data, and the analysis of biologic specimens. Finally, our broad network allows for the 25 enrollment of high numbers of patients with infections which are too rare for detailed study by 26 smaller, less diverse networks. We propose projects including monitoring of antimalarial 27 treatment responses, prevalence studies of strongyloidiasis in selected travellers and migrants, 28 and treatment intervention studies in the non-endemic setting. We describe the extensive 29 expertise, human and material resource we will marshal in order to continue our widely 30 recognized and successful programs.