Target-spike levels used in the construction of each specimen panel.

The format of each panel was the same. Samples were spiked with different microbes to represent varying levels of DNA and RNA for subsequent NA extraction: +++ high spike (Ct 18 ± 1.5); ++ medium spike (Ct 26 ± 1.5); + low spike (Ct 35 ± 1.5);–no spike.