[1] Columbia Univ, Coll Phys & Surg, Gertrude H Sergievsky Ctr, 622 West 168th St,PH 19-113, New York, NY 10032 USA
[2] Columbia Univ, Mailman Sch Publ Hlth, Dept Epidemiol, New York, NY 10032 USA
[3] Univ Witwatersrand, Fac Hlth Sci, Rahima Moosa Mother & Child Hosp, Dept Paediat & Child Hlth,Empilweni Serv, Johannesburg, South Africa
[4] Univ Witwatersrand, Fac Hlth Sci, Rahima Moosa Mother & Child Hosp, Dept Paediat & Child Hlth,Res Unit, Johannesburg, South Africa
[5] Univ Witwatersrand, Chris Hani Baragwanath Hosp, Perinatal HIV Res Unit, Johannesburg, South Africa
[6] Columbia Univ, Mailman Sch Publ Hlth, ICAP Columbia, New York, NY 10032 USA
[7] Columbia Univ, Dept Pediat, Coll Phys & Surg, New York, NY 10032 USA
[8] Columbia Univ, Mailman Sch Publ Hlth, Dept Biostat, New York, NY 10032 USA
[9] Columbia Univ, Div Infect Dis, Dept Med, Coll Phys & Surg, New York, NY 10032 USA