Yang 2020d.

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 diagnosis Design: diagnostic case‐control study, retrospective multicentre with historic control group Recruitment: 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 2019 Exclusion criteria: cases: not specified controls: 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‐nCov Facility controls: influenza pneumonia Country: China Dates: 1 January 2020‐15 February 2020 Symptoms and severity: all patients in early stages of COVID‐19 or influenza pneumonia Demographics: M/F: cases 41/32, controls 30/18 mean age: cases 41.9, controls 40.4 Exposure 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