1. Department of Community Medicine, Faculty of Medicine, College of Medical Sciences, University of Calabar, Calabar, Nigeria
2. Medical Research Council/Wits University Rural Public Health and Health Transitions Research Unit (Agincourt), School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
3. Department of Gobal Health and Population, Harvard T. H. Chan School of Public Health, Harvard University, Boston, Massachusetts, USA