[1] Univ Utrecht Hosp, Dept Virol, NL-3584 CX Utrecht, Netherlands
[2] Diakonessenhuis Hosp, NL-3584 CX Utrecht, Netherlands
[3] Natl Inst Publ Hlth & Environm, NL-3720 BA Bilthoven, Netherlands
[4] St Elizabeth Hosp, Tilburg, Netherlands
[5] Danderyd Hosp, S-18288 Danderyd, Sweden
[6] Hop St Vincent de Paul, F-75674 Paris, France
[7] Manchester Royal Infirm, Manchester M13 9WL, Lancs, England
[8] Univ Manchester, Dept Pathol Sci, Manchester, Lancs, England
[9] Publ Hlth Lab, Newcastle Upon Tyne, Tyne & Wear, England
[10] John Radcliffe Hosp, Oxford OX3 9DU, England
[11] Univ Roma La Sapienza, Rome, Italy