1Research Institute for Health Sciences, Chiang Mai University, Chiang Mai, Thailand, and Henry M. Jackson Foundation, Rockville, Maryland 20850
2Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205.
3Research Institute for Health Sciences, Chiang Mai University, Chiang Mai, Thailand
4Henry M. Jackson Foundation, Rockville, Maryland 20850
5Northern Drug Treatment Center, Chiang Mai, Thailand
6Henry M. Jackson Foundation, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand
7Walter Reed Army Institute of Research, Silver Spring, Maryland 20910
8Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand