1. Department of Paediatrics, University of Calabar Teaching Hospital, PMB 1278, Calabar, Nigeria
2. Calabar Institute of Tropical Disease Research and Prevention, University of Calabar Teaching Hospital, P.O. Box 1211, Calabar, Nigeria
3. Department of Community Medicine, University of Calabar Teaching Hospital, PMB 1278, Calabar, Nigeria
4. Medical Research Council (UK), Fajara, P.O. Box 273, Banjul, Gambia