Piero Poletti, Marcello Tirani, Danilo Cereda, Filippo Trentini, Giorgio Guzzetta, Giuliana Sabatino, Valentina Marziano, Ambra Castrofino, Francesca Grosso, Gabriele Del Castillo, Raffaella Piccarreta, ATS Lombardy COVID-19 Task Force, Aida Andreassi, Alessia Melegaro, Maria Gramegna, Marco Ajelli, Stefano Merler
We quantified the probability of developing symptoms (respiratory or fever>=37.5 °C) and critical disease (requiring intensive care or resulting in death) of SARS-CoV-2 positive subjects. 4,326 contacts of SARS-CoV-2 index cases detected in Lombardy, Italy were analyzed, and positive subjects were ascertained via nasal swabs and serological assays. 69.1% of all infected individuals aged less than 60 years did not develop symptoms (95% confidence interval: 66.7-71.4%). The risk of symptoms increased with age. 6.9% of infected subjects older than 60 years had critical disease, with males at significantly higher risk.