1. Department of Clinical Tropical Medicine , Faculty of Tropical Medicine , Mahidol University , Bangkok 10400 , Thailand
2. Department of Medicine , Rajavithi Hospital , Bangkok 10400 , Thailand
3. Department of Tropical Hygiene , Faculty of Tropical Medicine , Mahidol University , Bangkok 10400 , Thailand
4. Hospital for Tropical Diseases, Faculty of Tropical Medicine , Mahidol University , Bangkok 10400 , Thailand
5. Chulabhorn Hospital , Bangkok 10210 , Thailand