[1] Univ Verona, Policlin Borgo Roma, Ist Patol Speciale Med, Cattedra Med Interna, I-37134 Verona, Italy
[2] Univ Milan, Ist Igiene, I-20122 Milan, Italy
[3] Univ Padua, Dipartimento Med Clin & Sperimentale, I-35100 Padua, Italy
[4] Osped Niguarda Ca Granda, AVIS, Serv Immunoematol & Trasfus, Milan, Italy
[5] Univ Brescia, Cattedra Igiene, I-25121 Brescia, Italy
[6] Univ Milan, Ist Virol, I-20122 Milan, Italy