1 Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium. Electronic address: rvandepas@itg.be.
2 Centre National de Formation et de Recherche en Santé Rurale de Maferinyah, Forécariah, Guinea.
3 Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium; Centre National de Formation et de Recherche en Santé Rurale de Maferinyah, Forécariah, Guinea; Department of Public Health, Gamal University of Conakry, Conakry, Guinea.
4 Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium.