[1] Univ Maryland, Inst Human Virol, Baltimore, MD 21201 USA
[2] Univ Maryland, Dept Microbiol & Immunol, Baltimore, MD 21201 USA
[3] NHLBI, Hematol Branch, NIH, Bethesda, MD 20892 USA
[4] IRCCS, Policlin San Matteo, Viral Diagnost Serv, Pavia, Italy