Fig. 3: Clinical evaluation of FND Ag-LFT assay.
a Sensitivity and specificity evaluation of FND Ag-LFT compared to RT-qPCR grouped by sample Ct values. Sensitivity = 100%, 95.1%, and 86.8% for Ct ≤ 25, Ct ≤ 30, and all samples, respectively. Specificity was 100% (b) Plot of 53 SARS-CoV-2 positive clinical nasal swab samples with FND-Ag test line signal plotted against clinical sample concentrations (copies/mL) determined by RT-qPCR (n = 3 test replicates, Supplementary Fig. 8). Circles with error bars show the means and standard deviations of copy number and FND signal for each clinical sample. The data was fitted to a symmetrical Bayesian linear regression with the errors-in-variables in x and y58 (solid black line with 95% credible interval as grey dashed lines) to account for uncertainty in copies/mL quantification from RT-qPCR and FND signal (Supplementary Fig. 9). Purple indicates FND true positive, purple outline indicates FND positive and AuNP negative, and grey outline indicates RT-qPCR positive and negative on the FND-Ag assay and AuNP assay. Red dashed line indicates FND Ag-LFT cut-off threshold set to give false positive and false negative rates of 5% using n = 37 negative clinical samples (biological replicates). The black dotted line indicates extrapolated threshold for AuNP assay. c ROC analysis of clinical swab samples using 37 SARS-CoV-2 negative control samples and 53 positive samples showing sensitivity and specificity trade-off across all samples and sub-categories of samples with Ct ≤ 25 and Ct ≤ 30. d Raw data plot of clinical nasal swab samples positive for other respiratory viruses. Black bar represents mean signal. Data points represent distinct clinical samples where n = 53 SARS-CoV-2 positive samples, n = 50 SARS-CoV-2 negative samples, n = 6 RSV positive samples, n = 6 Flu A positive samples, and n = 1 Rhino Virus positive sample (all biological replicates). One-way ANOVA and Dunnett’s post-hoc test was used to determine significance from SARS-CoV-2 negative samples, **** denotes p-value = 7.89 × 10-7 for SARS-CoV-2 positives, p-value = 1.00 for RSV + , FluA + , and RHINO virus + ; F = 9.367, DF = 103. Source data and statistical analysis provided as Source Data file.
