Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) appeared just over 7 months ago in Wuhan, China. Early reports from China indicated that although some cases are asymptomatic, 20% of COVID-19 cases follow a severe course, necessitating hospitalization, with a quarter of hospitalized patients requiring intensive care unit (ICU) facilities [1]. Later reports from China and other countries substantiated these data, although ICU admission rates, proportion of patients receiving invasive mechanical ventilation (IMV), and mortality rates differ considerably between studies [2]. The life-threatening form of respiratory failure, acute respiratory distress syndrome (ARDS) is a frequent complication in COVID-19 [3]. The severity of ARDS is classified into categories of mild, moderate, and severe, depending on the degree of hypoxemia [4]. Patients with moderate-tosevere ARDS require invasive mechanical ventilation (IMV) and have a poor prognosis [4]. The incidence of ARDS and specifically, moderate-to-severe ARDS, among COVID-19 patients is currently unknown [5]. We describe here the results of a survey of clinical studies reporting COVID-19-associated ARDS in hospitalized patients since the beginning of the COVID-19 pandemic in January until the end of July 2020. Our aim was to obtain a clearer picture of the incidence of COVID-19-associated ARDS in hospitalized patients on a global level, to better define the burden to healthcare systems and to inform critical care clinicians. This information should enable the prediction of requirements for hospital resources and thereby facilitate planning an appropriate and timely response in the future. We carried out regular searches of PubMed using combinations of the search terms “ARDS,”“COVID-19,”“clinical characteristics,”“clinical features,”“clinical findings,”“ICU,”“incidence,”“outcome,” and “prevalence”(last search July 31, 2020).

Over 1000 publications were retrieved from which only studies reporting consecutively hospitalized patients, and giving numbers for ARDS patients and outcomes, were selected. Meta-analyses were excluded. Seventeen studies reporting results from 2486 hospitalized COVID-19 patients in five countries fitted the inclusion criteria (Tables 1 and 2). Limitations are that seven studies did not define ARDS and only one study classified patients as mild, moderate, and/or severe; the patient sample is comparatively small: twelve of the studies had less than 200 patients. Furthermore, there was heterogeneity in types of data gathered by each research group, hence for many of the studies, patient numbers did not permit calculation of all parameters (Tables 1 and 2).