1 Institute for Infectious Diseases (IFIK), University of Bern, Friedbühlstrasse 51, CH-3001 Bern, Switzerland.
2 Clinic Hirslanden, Zurich, Switzerland.
3 Labormedizinisches Zentrum Dr Risch, Bern-Liebefeld and Buchs SG, Switzerland.
4 Institute for Infectious Diseases (IFIK), University of Bern, Friedbühlstrasse 51, CH-3001 Bern, Switzerland. Electronic address: andrea.endimiani@ifik.unibe.ch.