1. Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China, and Key Laboratory of Public Health Safety (Fudan University), Ministry of Education, Shanghai, China
2. Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden
3. Department of Microbiology, the Public Health Agency of Sweden, Solna, Sweden
4. Department of Infectious Diseases, Imperial College, London, United Kingdom