[1] Duke Univ, Inst Res, Dept Clin Res, Durham, NC 27706 USA
[2] Brigham & Womens Hosp, Boston, MA 02115 USA
[3] Sahlgrens Univ Hosp, S-41345 Gothenburg, Sweden
[4] Univ Hull, Kingston Upon Hull HU6 7RX, N Humberside, England
[5] Imperial Coll Sch Med, London, England
[6] London Sch Hyg & Trop Med, London WC1, England