1. 1Department for Infectious Disease Epidemiology, Robert Koch-Institut, Seestrasse 10, 13353 Berlin, Germany
2. 2Academy for Public Health, Düsseldorf, Germany
3. 3Department for Epidemiology/Disease Control, German Technical Cooperation Agency (GTZ), Eschborn, Germany
4. 4Zentrum für Lebensmittelwissenschaften Tierärztliche Hochschule, Hannover, Germany
5. 5Department of Epidemiology, GlaxoSmithKline Biologicals, Rixensart, Belgium