Sonoda 2021.

Study characteristics
Patient Sampling	Purpose: diagnosis of SARS‐CoV‐2 infection (mild COVID‐19 disease); to investigate the clinical symptoms to discriminate between COVID‐19 and non‐COVID‐19 cases among outpatients in GP clinics Design: cross‐sectional cohort study, retrospective data collection Recruitment: outpatients visiting the screening centre (GP clinic) Sample size: n = 360 (17 cases) Inclusion criteria: patients visiting the centre with suspicion of COVID‐19 (no definition of 'suspicion') Exclusion criteria: patients who didn't receive a RT‐PCR test
Patient characteristics and setting	Facility cases: positive RT‐PCR for SARS‐CoV‐2 Facility controls: negative RT‐PCR for SARS‐CoV‐2 Country: Japan Dates: 01 August 2020‐14 August 2020 Symptoms and severity: clinical spectrum of cases (n = 17) was 14 moderate, 2 moderate and 1 severe illness Demographics: mean age: cases 39.6 years, controls 41.2 years M%/F%: cases 58.8/41.2, controls 50.7/49.2 Exposure history: close contact to patients with COVID‐19: cases 13.3%, controls 8.1%
Index tests	Body temperature Headache Sore throat Dysgeusia Anosmia Nasal discharge Cough Sputum production Nausea/vomiting Diarrhoea Stomach ache Fatigue Shortness of breath Joint pain Myalgia Lack of appetite
Target condition and reference standard(s)	TC: SARS‐CoV‐2 infection RS: SARS‐CoV‐2 RT‐PCR test (nasal swab or saliva specimen)
Flow and timing	Timing not specified
Comparative
Notes	Funding: none declared
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
Did the study avoid inappropriate exclusions?	Unclear
Did the study avoid inappropriate inclusions?	Yes
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
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?	Unclear
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?		Unclear risk