1. Department of Infectious Diseases Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, England.
2. Disease Control and Elimination Theme, Medical Research Council Unit, Banjul, Gambia.
3. Clinical Services Department, Medical Research Council Unit, Banjul, Gambia.
4. Vaccinology Theme, Medical Research Council Unit, Banjul, Gambia.
5. Mycobacteriology Unit, Institute of Tropical Medicine, Antwerp, Belgium.