1. International Maternal and Child Health, Department of Women's and Children's Health, Uppsala University, Uppsala University Hospital, SE 75185, Sweden.
2. Centro de Investigación en Demografía y Salud, UNAN-León, Parque Iglesia La Merced 1/2 cuadra al Oeste, León, Nicaragua.
3. Department of Disease Control, London School of Hygiene & Tropical Medicine, London, UK.