[1] Univ Witwatersrand, Fac Hlth Sci, Sch Publ Hlth, MRC Wits Rural Publ Hlth & Hlth Transit Res Unit, Johannesburg, South Africa
[2] Univ N Carolina, Gillings Sch Global Publ Hlth, Dept Epidemiol, Chapel Hill, NC 27516 USA
[3] Univ N Carolina, Carolina Populat Ctr, Chapel Hill, NC 27516 USA
[4] Univ Edinburgh, Coll Med & Vet Med, Edinburgh, Midlothian, Scotland
[5] Natl Inst Communicable Dis, Ctr Resp Dis & Meningitis, Natl Hlth Lab Serv, Johannesburg, South Africa
[6] Univ Witwatersrand, Fac Hlth Sci, Sch Publ Hlth, Johannesburg, South Africa