1. Haartman Institute, University of Helsinki, Department of Bacteriology and Immunology, P.O. Box 21, 00014 Helsinki, Finland
2. Helsinki University Hospital Laboratory, HUSLAB, Departments of Bacteriology and of Virology and Immunology, Haartmaninkatu 3, P.O. Box 400, Fl-00029 HUS, Helsinki, Finland
3. Haartman Institute, University of Helsinki, Department of Virology, P.O. Box 21, 00014 Helsinki, Finland
4. Eastern Finland Laboratory Centre Joint Authority Enterprise (ISLAB), Mikkeli District Laboratory, Porrassalmenkatu 35-37, 50100 Mikkeli, Finland