Review articles synthesize in narrative form the best available evidence on a topic. Review articles are only
published as part of Supplements to PLOS Medicine and are not featured in the PLOS Medicine Magazine.
Department of Global Health and Population, Harvard School of Public Health, Boston, Massachusetts, United States of America,
Africa Centre for Health and Population Studies, University of KwaZulu-Natal, Mtubatuba, KwaZulu-Natal, South Africa