Rentsch 2020.

Study characteristics
Patient Sampling	Purpose: diagnosis SARS‐CoV‐2 test positives Design: cross‐sectional, retrospective study Recruitment: electronic health record data from the national Veterans Affairs Healthcare System ‐ national Corporate Data Warehouse (USA) Sample size: 3789 (585 cases) Inclusion criteria: all patients in the Veterans Affairs cohort, born between 1945 and 1965 and active in care, tested for COVID‐19 between 8 February and 30 March 2020 Exclusion criteria: patients for whom results were pending (n = 93) or inconclusive (n = 33) were excluded
Patient characteristics and setting	Facility cases: tested positive for SARS‐CoV‐2 Facility controls: tested negative for SARS‐CoV‐2 Country: USA Dates: 8 February 2020‐30 March 2020 Symptoms and severity: all patients who were tested were included Demographics: median age overall: 65.7 years (IQR 60.5‐70.7) (cases: 66.1 years, controls: 65.6 years); gender overall (M%/F%): 90.2/9.8, cases 95.4/4.6, controls 89.2/10.8 Exposure history: not specified (all over USA)
Index tests	Hypoxia (oxygen saturation ≤ 93%) Body temperature (3 categories)
Target condition and reference standard(s)	TC: SARS‐CoV‐2 infection RS: no data on reference PCR test used, multiple different reference tests used with unknown test characteristics (samples: nasopharyngeal swabs)
Flow and timing	Time interval maximum 2 days
Comparative
Notes
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?	Yes
Did the study avoid inappropriate exclusions?	Yes
Did the study avoid inappropriate inclusions?	Unclear
Could the selection of patients have introduced bias?		Low risk
Are there concerns that the included patients and setting do not match the review question?			Unclear
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?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Unclear 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?	Unclear
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?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and Timing
Was there an appropriate interval between index test and reference standard?	Yes
Did all patients receive the same reference standard?	Unclear
Were all patients included in the analysis?	No
Could the patient flow have introduced bias?		Low risk