G Kampf1, M Exner2, I Schwebke3, J Gebel2. 1. University Medicine Greifswald, Institute for Hygiene and Environmental Medicine, Greifswald, Germany. Electronic address: guenter.kampf@uni-greifswald.de. 2. University Bonn, Institute for Hygiene and Public Health, Bonn, Germany. 3. Robert Koch Institute, Berlin, Germany.