Ide 2021.

Study characteristics
Patient Sampling	Purpose: diagnosis of SARS‐CoV‐2 infection (mild COVID‐19 disease) ‐ to evaluate the SARS‐CoV‐2‐positive ratio among mildly ill patients in Tokyo, Japan, their characteristics, the Ministry of Health, Labour and Welfare criteria, and to identify better criteria Design: cross‐sectional cohort study, retrospective data collection Recruitment: patients who underwent SARS‐CoV‐2 PCR testing at the National Center for Global Health and Medicine in Tokyo (= outpatient screening centre) Sample size: n = 277 (25 cases) Inclusion criteria: those who met ≥ 1 of the following criteria were eligible: patients who have fever or symptoms (e.g. respiratory, fatigue, headache, myalgia); patients who had exposure to COVID‐19 patient; patients who did not meet 1) or 2) but referred by another physician due to possible exposure to COVID‐19 patient or travel history. Exclusion criteria: patients who were non‐ambulatory upon presentation (referred to the infectious disease clinic for further evaluation)
Patient characteristics and setting	Facility cases: RT‐PCR‐positive for SARS‐COV‐2 Facility controls: RT‐PCR‐negative for SARS‐COV‐2 Country: Japan Dates: 09 March 2020‐29 March 2020 Symptoms and severity: mild to moderate severity Demographics: age: controls median 38.9 years, cases median 44.1 years M%/F%: cases 88.0/12.0, controls 52.0/48.0 Exposure history: exposure to case: cases 52%, controls 7%; travel: cases 72%, controls 20%
Index tests	Fever (> 37.5 °C) Nasal discharge Sore throat Cough Sputum Dyspnoea Fatigue Headache Myalgia/joint pain Diarrhoea Vomiting
Target condition and reference standard(s)	TC: SARS‐CoV‐2 infection RS: RT‐PCR, nasopharyngeal swabs
Flow and timing	Timing not specified
Comparative
Notes	Funding: grant for International Health Research from the Ministry of Health Labor and Welfare of Japan (grant no. 20A2003D)
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?	No
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?			Low concern
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?		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