1. These authors contributed equally to this article and share first authorship
2. Agency for Health Protection of Metropolitan Area of Milan (ATS), Milan, Italy
3. Direzione Generale Welfare, Unità Organizzativa Prevenzione, Lombardy Region, Milan, Italy
4. Department of Laboratory Medicine, Hospital Niguarda, Milan, Italy
5. Department of Biomedical Sciences for Health, Post Graduate School in Public Health, University of Milan, Milan, Italy
6. Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy
7. Department of Infectious Diseases, Istituto Superiore di Sanità, Rome, Italy