Study characteristics Patient Sampling Purpose: to identify differences in CT imaging and clinical features between COVID‐19 and
influenza pneumonia in the early stage, and to identify the most valuable features in the differential
diagnosisDesign: diagnostic case‐control study, retrospective multicentre with historic control groupRecruitment: cases: confirmed SARS‐CoV‐2 patients; controls: influenza pneumonia patients (1 January 2015‐30 September 2019 from 2 hospitals)Sample size: n = 121 (cases = 73)Inclusion criteria: patients confirmed with SARS‐CoV‐2; controls: patients who had 9 respiratory pathogen IgM antibody tested from January 2015‐September 2019Exclusion criteria: cases: not specifiedcontrols:parainfluenza respiratory syncytial virus adenovirus Legionella spp Mycoplasma pneumoniae Chlamydia pneumoniae Coxiella burnetii aspiration pneumonia radiation pneumonia pulmonary contusion pulmonary oedema neoplasm No CT date, no clinical date Patient characteristics and setting Facility cases: positive RT‐PCR for 2019‐nCovFacility controls: influenza pneumoniaCountry: ChinaDates: 1 January 2020‐15 February 2020Symptoms and severity: all patients in early stages of COVID‐19 or influenza pneumoniaDemographics: M/F: cases 41/32, controls 30/18
mean age: cases 41.9, controls 40.4Exposure history: not specified Index tests Body temperature Cough Fatigue Sore throat Stuffy and runny nose Target condition and reference standard(s) TC: COVID‐19 pneumonia RS: RT‐PCR (sample not specified) Flow and timing Time interval unclear Comparative   Notes Overlaps with Chen X 2020 Methodological quality Item Authors' judgement Risk of bias Applicability concerns DOMAIN 1: Patient Selection Was a consecutive or random sample of patients enrolled? Yes     Was a case‐control design avoided? No     Did the study avoid inappropriate exclusions? Unclear     Did the study avoid inappropriate inclusions? No     Could the selection of patients have introduced bias?   High risk   Are there concerns that the included patients and setting do not match the review question?     High DOMAIN 2: Index Test (All tests) Were the index test results interpreted without knowledge of the results of the reference standard? Unclear     If a threshold was used, was it pre‐specified? No     Could the conduct or interpretation of the index test have introduced bias?   High risk   Are there concerns that the index test, its conduct, or interpretation differ from the review question?     Low concern DOMAIN 3: Reference Standard Is the reference standards likely to correctly classify the target condition? Yes     Were the reference standard results interpreted without knowledge of the results of the index tests? Unclear     Could the reference standard, its conduct, or its interpretation have introduced bias?   High risk   Are there concerns that the target condition as defined by the reference standard does not match the question?     High DOMAIN 4: Flow and Timing Was there an appropriate interval between index test and reference standard? Unclear     Did all patients receive the same reference standard? Yes     Were all patients included in the analysis? Yes     Could the patient flow have introduced bias?   Unclear risk