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Incidence of ARDS and outcomes in hospitalized patients with COVID-19: a global literature survey

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-to-severe 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).

Table 1 Incidence of ARDS, ICU admission, IMV treatment, and outcome in hospitalized COVID-19 patients
Table 2 Incidence of ARDS, IMV treatment, and outcomes in COVID-19 patients admitted to an ICU

There is variability between individual studies with respect to frequency of ARDS, rates of ICU admission, and mortality among patients. Calculation of weighted averages for these parameters incorporating data from individual studies for which data is available indicate that among hospitalized COVID-19 patients, approximately 1/3 (33%) develop ARDS, 1/4 (26%) require transfer to an ICU, 1/6 (16%) receive IMV, and 1/6 (16%) die (Table 1). For COVID-19 patients transferred to an ICU, nearly 2/3 (63%) receive IMV and 3/4 (75%) have ARDS (Table 2). The mortality rate of ICU COVID-19 patients is 40% and of those who receive IMV 59%; the mortality rate in COVID-19-associated ARDS is 45%, and the incidence of ARDS among non-survivors of COVID-19 is 90% (Table 2). The high incidence of ARDS among COVID-19 patients revealed in our survey is consistent with the results of postmortem examinations of patients with COVID-19, in which the predominant finding is diffuse alveolar damage, the most frequent histopathologic correlate of ARDS.

For as long as there is neither a safe and efficacious vaccine nor therapy for severely affected COVID-19 patients, standard supportive care with lung-protective mechanical ventilation will be the cornerstone of treatment for these patients [5, 6]. The implications of these survey results are important and demonstrate the considerable challenges posed by the “COVID-19 crisis” to ICU practitioners, hospital administrators, and health policy makers.

Susan Tzotzos, MSc, PhD

Bernhard Fischer, PhD

Hendrik Fischer, PhD

Markus Zeitlinger, MD, PhD

Availability of data and materials

Data generated or analyzed during this study are included in this published article.



Acute respiratory distress syndrome


Coronavirus disease 2019


Intensive care unit


Invasive mechanical ventilation


Coronavirus 2


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This study received funding support from the European Commission (EC), Grant No. 101003595 and from the Austrian Research Promotion Agency (FFG), Grant No.880862.

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SJT conducted the literature search and survey. SJT, BF, and HF evaluated and contributed to the interpretation and presentation of the data. SJT drafted the manuscript; BF, HF, and MZ revised the final version of the manuscript. The authors read and approved the final manuscript.

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Correspondence to Susan J. Tzotzos.

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Tzotzos, S.J., Fischer, B., Fischer, H. et al. Incidence of ARDS and outcomes in hospitalized patients with COVID-19: a global literature survey. Crit Care 24, 516 (2020).

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