[1] Univ Rochester, Dept Emergency Med, Rochester, NY 14642 USA
[2] Univ Rochester, Dept Biostat, Rochester, NY 14642 USA
[3] Univ Witwatersrand, Perinatal HIV Res Unit, Chris Hani Baragwanath Hosp, Diepkloof, South Africa
[4] Univ Cape Town, Inst Infect Dis & Mol Med, Fac Hlth Sci, ZA-7925 Cape Town, South Africa