1 UNDP/UNFPA/UNICEF/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, Department of Reproductive Health and Research, WHO, Geneva 1211, Switzerland. Electronic address: kimca@who.int.
2 Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
3 Division of Sexually Transmitted Disease Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA.
4 National Institute of Allergy and Infectious Diseases, Rockville, MD, USA.
5 London School of Hygiene & Tropical Medicine, London, UK.
6 UNDP/UNFPA/UNICEF/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, Department of Reproductive Health and Research, WHO, Geneva 1211, Switzerland.