1. Department of Infectious Diseases, Tropical Medicine, and AIDS, Division of Internal Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
2. Department of Pathology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
3. Department of Virology, Erasmus Medical Center (EMC), Rotterdam, The Netherlands.
4. National Institute of Public Health and the Environment (RIVM), Bilthoven, The Netherlands.