[1] Univ North Carolina Chapel Hill Project China, 2 Lujing Rd, Guangzhou 510095, Guangdong, Peoples R China
[2] Univ North Carolina Chapel Hill, Sch Med, SESH Res Team, Guangzhou, Guangdong, Peoples R China
[3] Loyola Univ Chicago, Stritch Sch Med, Maywood, IL USA
[4] Univ North Carolina Chapel Hill, Sch Med, Chapel Hill, NC USA
[5] Guangdong Prov Ctr Skin Dis & Sexually Transmitte, Guangzhou, Guangdong, Peoples R China
[6] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA