Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.Division of Hematology, Department of Medicine, Rajavithi Hospital, Bangkok, Thailand.Division of Hematology, Department of Medicine, Rajavithi Hospital, Bangkok, Thailand.Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.Division of Hematology, Department of Medicine, Rajavithi Hospital, Bangkok, Thailand.