1. Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University , Bangkok, Thailand
2. Department of Medical Technology and Clinical Pathology, Mukdahan Hospital , Mukdahan, Thailand
3. Department of Medicine, Mukdahan Hospital , Mukdahan, Thailand
4. Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University , Bangkok, Thailand