Mertens 2020.

Study characteristics
Patient Sampling	Single‐group study to estimate sensitivity and specificity for diagnosis of active disease: ‐ samples from patients suspected of SARS‐COV‐2 infections (n = 328) Recruitment: random sampling of samples submitted to 3 laboratories 322/328 NP samples (NP swabs) were randomly selected Prospective or retrospective: retrospectively Number of samples (samples with confirmed SARS‐CoV‐2): 328 (132)
Patient characteristics and setting	Setting: unclear; samples from university laboratories (discussion states that no outpatient population has been sampled, therefore assume inpatients and HCW samples) Location: laboratories at Université Libre de Bruxelles (LHUB‐ULB), UZ Leuven and Centre Hospitalier Universitaire Sart‐Tilman (CHU) Liège Country: Belgium Dates: 19‐30 March 2020 Symptoms and severity: not reported Demographics: not reported Exposure history: unclear; 53/328 samples were from HCW
Index tests	Test name: COVID‐19 Ag Respi‐Strip Manufacturer: Coris BioConcept (Belgium) Antigen target: SARS‐CoV and SARS‐CoV‐2 highly conserved nucleoprotein Antibody: monoclonal antibodies directed against SARS‐CoV and SARS‐CoV‐2 highly conserved nucleoprotein antigen Test method: immunochromatographic assay using colloidal gold (CGIA) Samples used: remnant respiratory specimens (322 NP swabs, 4 NP aspirate and 2 BAL) Transport media: NP: flocked swab + UTM 3 mL (or 1 mL of Amies) (Copan, Brescia, Italy); NPA: 3 mL VTM (veal infusion broth (Difco, Becton Dickinson, Sparks, MD, USA) supplemented with bovine albumin (Sigma Aldrich, St Louis, MO, USA)) BAL: N/A Sample storage: not described Test operator: laboratory technician Definition of test positivity: visible reddish‐purple band appearing at the Test line position (T) Blinding reported: not stated Timing of samples: not clear
Target condition and reference standard(s)	Reference standard: qRT‐PCR: RealStar SARS‐CoV‐2 RT‐PCR Kit from Altona‐diagnostics with a cut‐off set at 40 Ct (LHUB‐ULB); Roche LC480 thermocycler using Taqman Fast Virus 1‐Step Master Mix (Thermo Fisher) (Liege); QuantStudio Dx (Thermo Fisher Scientific) or Panther Fusion (PF, Hologic, San Diego, USA) (UZ Leuven) Definition of non‐COVID cases: Genetic target(s): RealStar: not stated; Taqman Fast Virus: RdRp and E genes QuantStudio Dx; "slightly adapted" E‐gene Panther Fusion: E gene and ORF1‐ab Samples used: as for index test (respiratory specimens (322 NP swabs, 4 NP aspirate and 2 BAL) Timing of reference standard: not stated; same samples as for index test but analysed at time of collection Blinded to index test: yes (undertaken for diagnostic purposes at time of collection) Incorporated index test: no
Flow and timing	Time interval between index and reference tests: same samples used; discussion report 'some delay' between PCR and antigen testing All participants received same reference standard: yes but different RT‐PCR kits Missing data: no Uninterpretable results: none reported; discussion reports some difficulties in visualising the strip through the closed tube requiring the lab technician to open the test tube in the laminar air flow cabinet and pull out the strip with forceps Indeterminate results (index test): weak T lines considered positive Indeterminate results (reference standard): none reported; sensitivity can be extracted for cases with Ct values < or > 25 (high vs lower viral load) Unit of analysis: refers to participants
Comparative
Notes	Funding: not stated Publication status: preprint (not peer‐reviewed) Sourcepreprint server (medRxiv) Author COI: the IVD medical device has been developed by the investigator Pascal Mertens, Henri Magein, and Justine Bouzet working for Coris BioConcept (potential conflict of interest declared even though they don’t have any share in this company); Thierry Leclipteux was involved in the development of this test and is the CEO of Coris Bioconcept (potential conflict of interest declared). All scientific investigators that are external to Coris BioConcept declare having no conflict of interest.
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?	Yes
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?			High
DOMAIN 2: Index Test (Antigen 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?			High
DOMAIN 2: Index Test (Rapid PCR tests)
DOMAIN 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	No
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Reference standard does not incorporate result of index test?	Yes
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?	Yes
Did all patients receive the same reference standard?	Yes
Were all patients included in the analysis?	Yes
Did all participants receive a reference standard?	Yes
Were results presented per patient?	Yes
Could the patient flow have introduced bias?		Low risk