Endemic coronavirus in children and adults with acute respiratory infection before the COVID-19 pandemic.

Acute respiratory infection (ARI) is one of the principal causes of morbidity worldwide, with respiratory viruses being common etiological agents. Among them, endemic human coronaviruses (hCoVs) including CoV-229E, CoV-OC43, CoV-NL63, and CoV-HKU1 can cause mild ARI but are usually not evaluated in the clinical setting. The aim of this work was to determine the prevalence of all respiratory pathogens, with the focus placed on endemic hCoVs in the pre-pandemic period. Circulating species, clinical associations and coinfections with other respiratory pathogens were evaluated in 510 immunocompetent patients (children and adults) with ARI using the FilmArray® Respiratory Panel (BioFire/bioMérieux). A total of 399 children (252 outpatients and 147 hospitalized) and 111 adult outpatients were enrolled in the pre-pandemic period (2008-2010 and 2016). Endemic hCoVs were the third and fifth more frequently detected viruses among adults and outpatient children, respectively, with an overall frequency close to 10%. The most prevalent species were CoV-OC43 (42.8%) and CoV-HKU1 (40.5%), followed by CoV-NL63 (19.0%) and CoV-229E (4.8%). Tachypnea, wheezing and chest indrawing were more frequent in hospitalized children compared to outpatients. All adult patients presented with symptoms of a common cold. Endemic hCoVs were detected year-round, primarily between June and November. Our results highlight their clinical relevance, and the need to include endemic hCoVs in routine screening. In the post-pandemic period, further long-term surveillance is needed for understanding the epidemiology of endemic hCoVs and their evolution, as a tool to anticipate the possible emergence of new species.