Dynamics of endemic human coronavirus and SARS-CoV-2 in a hospital of Madrid, Spain. Retrospective study from June 2020 to July 2023.

An observational and retrospective study was carried out to analyse HCoV positivity from a multiplex PCR respiratory panel and RT-PCR for SARS-CoV-2 in respiratory samples from 1 June 2020 to 31 July 2023 at the Príncipe de Asturias University Hospital (HUPA) in Alcalá de Henares, Madrid, Spain. Out of 2802 respiratory panels, 1258 (44.8%) turned out positive. HCoV was detected in 114 (4%) cases (range 0-23; median 1.5; IQR 0-3.75) with positivity rates ranging from 0% to 14%. All four variants of HCoV circulated, and OC-43 was the most common in 62.3% of cases. After the onset of the pandemic, the HCoV season was delayed 22 weeks, with a peak positivity of 9% in the summer of 2021, showing an inverse relationship with the alpha and delta waves of SARS-CoV-2. In the two subsequent autumn-winter seasons, HCoV positivity increased (11-14%) with a reduction in the summer of 2022 and 2023 following the emergence of the omicron variant and the relaxation of social distancing measures. The seasonal spread pattern of endemic HCoV might be returning to normal in our region and likely in other temperate zones of the northern hemisphere after 3 years of the pandemic.