2.2. Patients
All participants were COVID-19-RT-PCR-positive subjects who required more than 48 h of hospital admission to the Internal Medicine Service of Sagunto Hospital, Valencia, Spain. Nasopharyngeal samples were collected on the first day of admission for RT-PCR analysis using the VERSANT PCR Molecular System (Siemens, Munich, Germany). Exclusion criteria were age <18 years and hospital discharge in the first 48 h. 