1. London School of Hygiene and Tropical Medicine, London, United Kingdom;
2. National Hospital Abuja, Nigeria, Abuja, Nigeria;
3. University of Abuja Teaching Hospital, Gwagwalada, Nigeria;
4. University of Nigeria Teaching Hospital, Enugu, Nigeria;
5. Asokoro District Hospital, Abuja, Nigeria;
6. Garki Hospital, Abuja, Nigeria;
7. Wuse General Hospital, Abuja, Nigeria;
8. Department of Epidemiology and Public Health,School of Medicine & Institute of Human Virology, University of Maryland, Baltimore, MD;
9. International Agency for Research on Cancer, Lyon, France;