[1] Ctr Dis Control & Prevent, Div STD Prevent, Natl Ctr HIV STD & TB Prevent, Atlanta, GA 30333 USA
[2] Massachusetts Gen Hosp, Dept Pathol, Boston, MA 02114 USA
[3] Univ Hosp Coimbra, Dept Pathol, Coimbra, Portugal
[4] Univ Porto, Inst Mol Pathol & Immunol, P-4100 Oporto, Portugal
[5] Fac Med HS Joao, Oporto, Portugal