1. Department of Social and Environmental Medicine , Faculty of Tropical Medicine, , Bangkok , Thailand
2. Mahidol University , Faculty of Tropical Medicine, , Bangkok , Thailand
3. Thai Travel Clinic , Hospital for Tropical Diseases, Faculty of Tropical Medicine, , Bangkok , Thailand
4. Mahidol University , Hospital for Tropical Diseases, Faculty of Tropical Medicine, , Bangkok , Thailand
5. Division of Epidemiology , Department of Public Health Sciences, , Davis, CA , USA
6. University of California Davis School of Medicine , Department of Public Health Sciences, , Davis, CA , USA
7. Department of Microbiology and Immunology , Faculty of Tropical Medicine, , Bangkok , Thailand
8. Mahidol-Oxford Tropical Medicine Research Unit , Faculty of Tropical Medicine, , Bangkok , Thailand
9. Department of Clinical Tropical Medicine , Faculty of Tropical Medicine, , Bangkok , Thailand
10. Department of Microbiology , Faculty of Public Health, , Bangkok , Thailand
11. Mahidol University , Faculty of Public Health, , Bangkok , Thailand
12. Center for Tropical Medicine & Global Health , Nuffield Department of Medicine, , Oxford , UK
13. Oxford University , Nuffield Department of Medicine, , Oxford , UK
14. Travel Medicine Research Unit , Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, , Bangkok , Thailand
15. Mahidol University , Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, , Bangkok , Thailand