Fig. 3.

Probit analysis sigmoid curve reporting the LoD of each assay. Replicate reactions of ORF1ab (a) and N gene (b) of qRT-PCR, ORF1ab (c) and N gene (d) of OSN-qRT-PCR and ORF1ab (e) and N gene (f) of ddPCR were done at concentrations around the detection end point determined in preliminary dilution experiments. The X axis shows expected concentration (copies/ml). The Y axis shows fraction of positive results in all parallel reactions performed. The inner line is a probit curve (dose–response rule). The outer lines are 95% confidence interval (95% CI). Data are representative of three independent experiments with 14 replicates for each concentration