Figure 4

Determination of the LOD for MP4 assay. LOD was determined in single-sample (a-c) and pooled (d) assays using three different SARS-CoV-2 virus sources. LOD for QE-extracted virus in water (a) and purified viral RNA diluted in water (b) and were determined to be 2 and 1 SARS-CoV-2 copies per µl, respectively. The LOD in single-sample (c) and pooled (d) assays in which negative saliva was spiked with a positive saliva sample of known virus concentration was determined to be 2 and 12 SARS-CoV-2 copies per µl, respectively. Experiments in (c,d) were performed using PK-digested saliva according to the MP4 assay. Data points above the dotted line (set at 2 copies per µl) meet our threshold of ≥ 3 positive N1 droplets. LOD is represented as SARS-CoV-2 copies per µl in the starting sample and was defined as the lowest concentration of virus in which ≥ 95% of replicates (n ≥ 20) were scored as positive.