1. Department of Epidemiology Research, Division of Health Surveillance and Research, Statens Serum Institut, Copenhagen, Denmark
2. Division of Infection Medicine, Skåne University Hospital and Department of Clinical Sciences Lund, Lund University, Lund, Sweden
3. Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden
4. Department of Medicine, Stanford University School of Medicine, Stanford, California