[1] Inst Trop Med, HIV STI Unit, Natl Str 155, B-2000 Antwerp, Belgium
[2] Inst Trop Med, HIV STD Unit, Antwerp, Belgium
[3] Ohio State Univ, Coll Publ Hlth, Nationwide Childrens Hosp, Res Inst, Columbus, OH 43210 USA
[4] Univ Maryland, Sch Med, Inst Genome Sci, Dept Epidemiol & Publ Hlth, Baltimore, MD 21201 USA