[1] Univ Cape Town, Dept Publ Hlth, ZA-7700 Rondebosch, South Africa
[2] Univ Cape Town, Dept Paediat, ZA-7700 Rondebosch, South Africa
[3] Univ Cape Town, Dept Child Hlth, ZA-7700 Rondebosch, South Africa
[4] Univ Cape Town, Dept Virol, ZA-7700 Rondebosch, South Africa
[5] St Bartholomews & Royal Hosp, London Sch Med, London, England