1. Epidemiology Unit, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, Thailand
2. The First Peoples' Hospital of Kunming City, Yunnan, PR China
3. Yunnan Institute for Drug Abuse, Xi Hua Yuan, Kunming, Yunnan, PR China
4. Department of Infectious Diseases, The First Affiliated Hospital of Kunming Medical University, Yunnan, PR China