[1] Emory Univ, Sch Med, Atlanta, GA 30322 USA
[2] Atlanta VA Med Ctr, Res Serv 151I, Decatur, GA USA
[3] London Sch Hyg & Trop Med, London WC1, England
[4] Ullevaal Univ Hosp, Dept Paediat, Oslo, Norway
[5] Ullevaal Univ Hosp, Dept Clin Chem, Oslo, Norway
[6] Univ Oslo, Fac Med, Oslo, Norway