The study cohort will be enrolled among all Humanitas group employees (including ICH, Humanitas University and Gavazzeni), and two validation cohorts. Participants will be asked consent for the research use of blood, pharyngeal swab, and for those hospitalized for COVID-19, also for the bronchoalveolar lavage and fecal samples. Biological samples will be used to perform cellular, microbial and molecular analyses aimed at better understanding the disease pathogenesis and the individual differences in susceptibility to the disease.

The analysis will include:

• study the expression levels of molecules known to mediated viral infection, like the Angiotensin converting enzyme 2 (ACE2) and genetic variants in these genes, which could be related to susceptibility to the viral infection and/or to the severity of the clinical course of the disease
• compare the frequency of genetic variants potentially related with COVID-19 susceptibility/severity in different subgroups of patients, ranging from individuals positive for the virus but asymptomatic to individuals affected by COVID-19 with ARDS requiring admission to ICU
• germline DNA analysis to search for genetic factors predisposing or protecting against severe pulmonary affection in COVID-19 infected participants. To this aim DNA will be analyzed by a GWAS (Genome Wide Association Study) approach by using the GSA Illumina chip. The obtained data will also be used to try to develop a polygenic risk score to stratify individuals with a particularly high or low risk for severe disease course
• explore the contribution of rare variants by studying the exome
• sepsis and ARDS biomarkers developed at ICH (e.g. PTX3, sIL-1R2, MSF) analysis to address their prognostic potential in Covid-19 patients
• PBMC analysis by FACS to investigate the immunophenotype and correlate it to the clinical outcome
• microbiota analysis of residual BAL and pharyngeal swab to evaluate whether different microbial or metabolome profiles are associated to worsen disease or to protection
• plasma and saliva/sputum test for anti-SARS-Cov-2 antibodies (IgM, IgG, IgE and IgA) and for microbiota analysis

Inclusion Criteria:

• 1. Individuals aged ≥ 18 years;

Exclusion Criteria:

• 1. Lack of informed consent according to local procedure per critically ill patients.

The study cohort will be enrolled among all Humanitas group employees (including ICH, Humanitas University and Gavazzeni), and two validation cohorts