[1] Univ Witwatersrand, Fac Hlth Sci, Sch Publ Hlth, Johannesburg, South Africa
[2] South African Med Res Council, Hlth Syst Res Unit, Cape Town, South Africa
[3] Univ Zambia, Sch Med, Dept Obstet & Gynaecol, Lusaka, Zambia
[4] South Afr Med Res Council, Off President, Cape Town, South Africa
[5] Univ Zambia, Sch Publ Hlth, Lusaka, Zambia
[6] Charlotte Maxeke Johannesburg Acad Hosp, Dept Community Hlth, Johannesburg, South Africa