Wolff 2020 [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of current acute and convalescent‐phase infection Design: Multi‐group study to estimate sensitivity and specificity [1] Confirmed Covid patients (n = 111) [1a] Symptomatic Covid (n = 87) [1b] Asymptomatic Covid (n = 24) [2] Pre‐pandemic, non‐Covid (n = 96) Recruitment: Not stated. Prospective or retrospective: [1] Unclear [2] Retrospective Sample size: 207 (111) Further detail: [1] Included symptomatic (mild to moderate or severe) cases and asymptomatic cases confirmed by qRT‐PCR [1b] Asymptomatic patients were defined as individuals without any symptoms who were screened positive for SARS‐CoV‐2 nucleic acid due to close contacts with COVID‐19 patients. [2] Residual serum samples non‐SARS‐CoV‐2 collected before the pandemic COVID‐19 from January to February 2019 Exclusion criteria not stated
Patient characteristics and setting	Setting: Not stated (seems to be mixed) Location: Laboratoire Hospitalier Universitaire de Bruxelles, Université Libre de Bruxelles, Brussels, Belgium Country: Belgium Dates: Not stated Symptoms and severity: Mild to moderate (n = 47): fever, headache, cough, myalgia Severe (n = 40): need for oxygen supplementation, respiratory failure requiring mechanical ventilation, admission to ICU or death Asymptomatic (n = 24) Demographics: [1a] median age 60 years, range 21‐88 years, 36 women, 51 men [1b] median age 61 years, range 20‐85 years, 11 women, 13 men Exposure history: [1a] not stated [1b] close contacts of Covid cases Non‐Covid group 1: Pre‐pandemic, non‐Covid patients (n = 96) Source: Residual samples collected between January to February 2019. source not stated Characteristics: Median age 38, range 0 ‐87 years, 62 women, 38 men
Index tests	Test name: [A] Elecsys Anti‐SARS CoV‐2 [B] Liaison SARS‐CoV‐2 S1/S2 IgG [C] Euroimmun Anti‐SARS CoV‐2 IgG ELISA [D] Euroimmun Anti‐SARS CoV‐2 IgA ELISA [E] VIDAS Anti‐SARS CoV‐2 IgG [F] VIDAS Anti‐SARS CoV‐2 IgM Manufacturer: [A] Roche Diagnostics, Vilvoorde, Belgium [B] Diasorin, Saluggia, Italy [C] [D] Euroimmun, Luebeck, Germany [E] [F] BioMerieux, Marcy‐l'Etoile, France Antibody: [A] IgM/IgG (total antibodies including IgG) [B] IgG [C] IgG [D] IgA [E] IgG [F] IgM Antigen target: [A] N‐protein [B] S1/S2‐protein [C] [D] S1‐protein [E] [F] S‐protein Evaluation setting: Laboratory Test method: [A] CLIA [B] CLIA [C] [D] ELISA [E] [F] enzyme linked fluorescence assay (ELFA) Timing of samples: [1a] 0‐54 days pso [1b] 0‐15 days post‐PCR + 0–7 days post‐symptoms or post + PCR: n = 35 8–14 days post‐symptoms or post + PCR: n = 31 > 15 days post‐symptoms or post + PCR: n = 45 Samples used: Serum Test operator: Laboratory staff Definition of test positivity: [A] negative COI < 1, positive COI >= 1 [B] negative < 12 AU/mL, borderline >= 12 to < 15 AU/mL, positive >= 15 AU/mL [C] [D] negative < 0.8, borderline >= 0.8 to < 1.1, positive >= 1.1 [E] [F] negative (index < 1) or positive (index ≥ 1) Blinding reported: Unclear Threshold predefined: Yes, according to manufacturer
Target condition and reference standard(s)	Reference standard: qRT‐PCR using the RealStar SARS‐CoV‐2 RT‐PCR kit 1.0, threshold not stated Samples used: Not stated Timing of reference standard: Not stated Blinded to index test: Yes, prior Incorporated index test: No Definition of non‐COVID cases: Pre‐pandemic Samples used: NA, pre‐pandemic Timing of reference standard: NA, pre‐pandemic Blinded to index test: yes, prior Incorporated index test: no
Flow and timing	Time interval between index and reference tests: [1a] Not stated [1b] 0‐15 days post‐PCR + (n = 24) All patients received same reference standard: No, [2] pre‐pandemic Missing data: 45 samples 16‐54 days pso not included in review Uninterpretable results: Not stated Indeterminate results: Borderline data were found for [B] four samples analysed using the Liaison IgG, two samples using the [C] Euroimmun IgG and [D] IgA. Borderline data were considered positive for the statistical analyses. Unit of analysis: Patients
Comparative
Notes	Funding: Not stated Publication status: Published paper Source: Diagnostic Microbiology and Infectious Disease Author COI: No declaration of competing interest
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?	No
Did the study avoid inappropriate exclusions?	Unclear
Did the study avoid inappropriate inclusions?	Unclear
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)
DOMAIN 2: Index Test (Antibody 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?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
The reference standard does not incorporate the index test	Yes
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?			High
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?	No
Were all patients included in the analysis?	Yes
Did all participants receive a reference standard?	No
Were results presented per patient?	Yes
Could the patient flow have introduced bias?		High risk