Sun 2020a.

Study characteristics
Patient Sampling	Purpose: algorithm development for estimating risk COVID‐19 Design: cross‐sectional, retrospective study Recruitment: patients presenting at the designated national outbreak screening centre and tertiary care hospital in Singapore for SARS‐CoV‐2 testing. Patients were either self‐referred, referred from primary care facilities, or were at‐risk cases identified by national contact tracing efforts (recruited n = 991) Sample size: n = 788 (n = 54) Inclusion criteria: patients presenting to the centre: self‐referred referred from primary care facilities at‐risk cases identified by national contact tracing efforts Exclusion criteria: PCR results not available at time of data collection ‐ no electronic medical records ‐ unavailable vital sign records
Patient characteristics and setting	Facility cases: positive SARS‐CoV2 RT‐PCR test Facility controls: all SARS‐CoV‐2 RT‐PCR results were negative (minimum 2 test negatives in high‐risk patients, minimum 1 test low‐risk patients) Country: Singapore Dates: 26 January 2020‐16 February 2020 Symptoms and severity: 252 (33.2%) symptoms > 5 days at presentation, 75 (9.5%) any comorbidity body temperature heart rate respiratory rate systolic BP diastolic BP cough sputum production shortness of breath rhinnorhoea or nasal congestion sore throat auscultation finding of pneumonia other respiratory symptoms gastrointestinal symptoms Demographics: median age 34 years (range 7 years‐98 years, IQR 27‐45) (cases median 42 years, range 16‐79; controls 34 years (range 7‐98); M/F: 48.3%/51.7% F (cases M: 88 (88.9%)) Exposure history: contact with a known COVID‐19 case (20.1% (32/54 cases (59.3%)); 126/734 controls (17.2%), contact with travellers from China (22.1%, 15/54 cases (27.8%); 42/734 controls (5.7%)), recent travel history, and visit to hospital in China within 14 days prior to symptom onset (0.8%)
Index tests	Body temperature Heart rate Respiratory rate Systolic BP Diastolic BP Cough Sputum production Shortness of breath Rhinnorhea or nasal congestion Sore throat Auscultation finding of pneumonia Other respiratory symptoms GI symptoms
Target condition and reference standard(s)	TC: SARS‐CoV‐2 infection RS: SARS‐CoV‐2 2 commercial assays 2‐target (1 assay: Orf1ab and N ‐ other unclear) RT‐PCR
Flow and timing	Time interval not specified
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?	No
Did the study avoid inappropriate exclusions?	Yes
Did the study avoid inappropriate inclusions?	Yes
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?	Yes
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?	No
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low 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?	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?		Low risk