[1] Univ Cambridge, Dept Haematol, E Anglia Blood Ctr, Cambridge CB2 2PT, England
[2] Ctr Natl Hop Univ, Dept Microbiol, Cotonou, Benin
[3] Programme Natl Lutte Contre SIDA, Cotonou, Benin
[4] Natl Blood Serv, Cambridge, England
[5] Univ Cambridge, Dept Haematol, Div Transfus Med, Cambridge CB2 2PT, England