1. Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University , Bangkok 10400 , Thailand
2. Clinical Microbiology Department, Sunpasitthiprasong Hospital , Ubon Ratchathani 34000 , Thailand
3. Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford , OX3 7FZ , UK
4. Department of Tropical Hygiene, Faculty of Tropical Medicine, Mahidol University , Bangkok 10400 , Thailand