[1] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Epidemiol, Baltimore, MD USA
[2] Univ Witwatersrand, Fac Hlth Sci, Perinatal HIV Res Unit, Johannesburg, South Africa
[3] Populat Serv Int, Johannesburg, South Africa
[4] Johns Hopkins Univ, Sch Med, Ctr TB Res, Baltimore, MD USA