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Table 2 Included studies

From: Informing the public health response to COVID-19: a systematic review of risk factors for disease, severity, and mortality

Author Type of study Country Study population Overall number of patients Analytical method used Factors included in multivariable model Disease, disease severity, or death Definition of severity
Cai [19] Retrospective cohort China Hospitalised patients, single hospital 298 Univariable; logistic regression N/A; age, sex, comorbidities, clinical markers, travel history Disease severity As per the international guidelines for community-acquired pneumonia, with a scoring system based on demographics, comorbid illness, physical examination findings, and laboratory and radiographic findings
Chen [20] Retrospective cohort China Hospitalised patients, single hospital 249 Logistic regression Age, sex, comorbidities and a range of clinical measures Disease severity ICU admission
Chen [21] Retrospective cohort with a nested case-control study China Hospitalised patients (moderately, severely or critically ill), single hospital 274 Univariable N/A Death N/A
Chen [22] Case-control China COVID-19 vs. pneumonia negative for SARS-CoV-2 104 (78 COVID-19) Univariable N/A Disease N/A
Chen [23] Retrospective cohort China Hospitalised patients, single hospital 21 Univariable N/A Disease severity Severe meets any of the following criteria- respiratory distress, RR ≥ 30 breaths/min; SpO2 ≤ 93% at rest; and PaO2/FIO2 ≤ 300. Patients with greater than 50% lesion progression within 24 to 48 h in pulmonary imaging.
Cheng [24] Case-control China Patients presenting with fever diagnosed with pneumonia by specialists with chest CT scans 38 (11 COVID-19) Univariable N/A Disease N/A
Chinese CDC [25] Retrospective cohort China Nationwide surveillance 72,314 Univariable N/A Death N/A
Fan [26] Retrospective cohort Singapore Hospitalised patients, National Centre for Infectious Diseases 67 Univariable N/A Disease severity ICU admission
Grasselli [27] Prospective cohort with a nested case-control study Italy Hospitalised in ICU across 72 hospitals 1591 Univariable N/A Death N/A
Han [28] Retrospective cohort China Hospitalised patients, single hospital 273 Univariable N/A Disease severity Severe met at least one of the following conditions: a) shortness of breath, RR ≥ 30 times/min, b) oxygen saturation (resting state) ≤93%, or c) PaO2/FiO2 ≤ 300 mmHg., in addition to positive SARS-CoV-2 RNA nucleic acid test by Reverse transcription polymerase chain reaction, fever, or other respiratory symptoms (the typical CT image abnormities of viral pneumonia were optional). Critical patients also needed to meet at least one of the extra following conditions: a) respiratory failure that needs to receive mechanical ventilation; b) shock; and c) multiple organ failure that need to be transferred to the ICU.
Huang [29] Retrospective cohort China Hospitalised patients, single hospital 41 Univariable N/A Disease severity ICU admission
ICNARC [30] Case-control (disease) / Prospective cohort (disease severity) England, Northern Ireland and Wales Hospitalised patients in ICU across a network of hospitals 12,502 (6720 COVID-19) Univariable N/A Disease; Disease severity Receiving advanced, as opposed to basic, respiratory support
Liang [31] Prospective cohort China Hospitalised patients across 575 hospitals 1590 Logistic regression; Cox regression Logistic model adjusted for age, sex, smoking history, comorbidities, cancer Disease severity, Death Invasive ventilation, ICU admission, death
Liu [32] Retrospective cohort China Hospitalised patients, single hospital 119 Univariable N/A Disease severity Severe- dyspnoea accompanied by hypoxemia, sometimes acute respiratory distress syndrome, septic shock and multiple organ failure
Liu [33] Retrospective cohort China Hospitalised patients, single hospital 4880 Logistic regression Age, sex Disease N/A
Qiu [34] Retrospective cohort China Hospitalised paediatric patients, three hospitals 36 Univariable N/A Disease severity Moderate disease (mild was baseline)- mild pneumonia; symptoms such as fever, cough, fatigue, headache, and myalgia; no complications and manifestations related to severe conditions
Ruan [35] Retrospective cohort with a nested case-control study China Hospitalised patients across two hospitals with a definitive outcome 150 Univariable N/A Death N/A
Shi [36] Retrospective cohort China Hospitalised patients across a province 487 Univariable; logistic regression N/A; age, sex, hypertension; full list unknown Disease severity Severe pneumonia, characterised by fever, cough, dyspnoea, bilateral pulmonary infiltrates, and acute respiratory injury
Simmonet [37] Retrospective cohort France Hospitalised patients in ICU, single hospital 124 Logistic regression Age, sex, diabetes, hypertension, BMI Disease severity Receiving invasive mechanical ventilation, determined when oxygen therapy (≥ 10 L/min) with target SpO2 (90–94%) was ineffective, and when RR was above 25/min, with signs of acute respiratory failure, despite maximal oxygen therapy
Tian [38] Retrospective cohort China Hospitalised individuals transferred from the hospitals of Beijing to the designated hospitals for specialist treatment of infectious diseases by Beijing Emergency Medical Service 262 Univariable N/A Disease severity Severe- dyspnoea or respiratory failure in addition to fever, respiratory symptoms and radiographic evidence of pneumonia
Wan [39] Prospective cohort China Hospitalised patients, single hospital 135 Univariable N/A Disease severity Severe group- respiratory distress, RR ≥ 30 breaths/minute in a resting state, a mean oxygen saturation of ≤93%, and an PaO2/FiO2 ≤ 300 mmHg
Wang [40] Case-control China Country-wide data compared to historic SARS/MERS 11,425 (835 COVID-19) Univariable N/A Disease N/A
Wang [41] Retrospective cohort China Hospitalised patients, single hospital 138 Univariable N/A Disease severity ICU admission
Wang [42] Prospective cohort China Hospitalised patients, single hospital 116 Univariable N/A Disease severity Severe- fever or suspected respiratory infection, plus one of the following: RR > 30 breaths/min; severe respiratory distress; or SpO2 ≤ 93% on room air
Wang [43] Cross-sectional China Hospitalised patients, single hospital 69 Univariable N/A Disease severity SpO2 < 90%
Wu [44] Retrospective cohort China Hospitalised patients, single hospital 201 Univariable; Cox regression N/A Disease severity, Death ARDS, mechanical ventilation
Wu [45] Prospective cohort China Country-wide data 44,672 Univariable N/A Death N/A
Yang [46] Retrospective cohort China Hospitalised patients, single hospital, admitted to ICU 52 Univariable; Cox regression N/A Death N/A
Yuan [47] Retrospective cohort China Hospitalised patients, single hospital 27 Univariable N/A Death N/A
Zhang [48] Retrospective cohort China Hospitalised patients, single hospital 140 Univariable N/A Disease severity Severe COVID-19 was designated when the patients had one of the following criteria: (a) respiratory distress with respiratory frequency ≥ 30/min; (b) pulse oximeter oxygen saturation ≤ 93% at rest; and (c) oxygenation index (PaO2/FiO2) ≤ 300 mmHg.
Zhang [49] Retrospective cohort China Hospitalised patients (patients with no severe underlying diseases), single hospital 95 Univariable N/A Disease severity Severe- RR ≥ 30 times / min; at rest, oxygen saturation ≤ 93%; PaO2/FiO2 ≤ 300 mmHg
Zhang [50] Retrospective cohort China Hospitalised patients, single hospital 120 Univariable N/A Disease severity Severe- when patients met one of the following criteria: (1) respiratory distress with a breathing rate ≥ 30/min; (2) pulse oximeter oxygen saturation ≤ 93% at rest; (3) oxygenation index (PaO2/FiO2) ≤300 mmHg; (4) respiratory failure requiring mechanical ventilation; (5) shock; and (6) combined with other organ failure requiring ICU monitoring and treatment
Zhou [51] Retrospective cohort with a nested case-control study China Hospitalised patients across two hospitals with a definitive outcome 191 Univariable; logistic regression N/A; age, coronary heart disease, Sequential Organ Failure Assessment score, lymphocyte count, D-dimer Death N/A
  1. ARDS acute respiratory distress syndrome, BMI body mass index, CDC Center for Disease Control and Prevention, CT computed tomography, FiO2 inspired oxygen fraction, ICNARC intensive care national audit and research centre, ICU intensive care unit, MERS Middle Eastern Respiratory Syndrome, N/A not applicable, PaO2 arterial partial pressure of oxygen, RR respiratory rate, SARS severe acute respiratory syndrome, SpO2 oxygen saturation