1. Desmond Tutu HIV Centre, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
2. School of Child and Adolescent Health, University of Cape Town, Cape Town, South Africa.
3. Seattle Childrens' Hospital, University of Washington Pediatric Infectious Diseases, Seattle, Washington.
4. Network Dynamics Group, Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany.
5. Infectious Diseases Epidemiology Unit, School of Public Health and Family Medicine, University of Cape Town, Cape Town, South Africa.
6. Department of Epidemiology, Mailman School of Public Health, Columbia University, New York.