Probability of symptoms and critical disease after SARS-CoV-2 infection

TL;DR

This study estimates the probabilities of symptoms and critical disease among SARS-CoV-2 positive individuals, highlighting age and gender differences in disease severity based on a large contact tracing dataset from Italy.

Contribution

It provides quantitative estimates of symptom development and critical disease risk stratified by age and gender in a large Italian cohort.

Findings

73.9% of infected under 60 years old remained asymptomatic.

6.6% of infected over 60 years developed critical disease.

Higher risk of critical disease observed in males over 60.

Abstract

We quantified the probability of developing symptoms (respiratory or fever \geq 37.5 {\deg}C) and critical disease (requiring intensive care or resulting in death) of SARS-CoV-2 positive subjects. 5,484 contacts of SARS-CoV-2 index cases detected in Lombardy, Italy were analyzed, and positive subjects were ascertained via nasal swabs and serological assays. 73.9% of all infected individuals aged less than 60 years did not develop symptoms (95% confidence interval: 71.8-75.9%). The risk of symptoms increased with age. 6.6% of infected subjects older than 60 years had critical disease, with males at significantly higher risk.