1. Thai Travel Clinic , Hospital for Tropical Diseases, Faculty of Tropical Medicine, , Bangkok , Thailand
2. Mahidol University , Hospital for Tropical Diseases, Faculty of Tropical Medicine, , Bangkok , Thailand
3. Department of Clinical Tropical Medicine , Faculty of Tropical Medicine, , Bangkok , Thailand
4. Mahidol University , Faculty of Tropical Medicine, , Bangkok , Thailand
5. Travel Medicine Research Unit , Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, , Bangkok , Thailand
6. Mahidol University , Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, , Bangkok , Thailand
7. Mahidol-Oxford Tropical Medicine Research Unit , Faculty of Tropical Medicine, , Bangkok , Thailand