We realised soon that the SARS-CoV E gene assay was more sensitive than the two RdRp gene assays combined with the one-step RT-PCR system available in our laboratory. However, our E gene assay showed high background levels hampering a clear evaluation of the assays. Each mastermix has its own proprietary composition, which may explain the differences in the performance of a certain PCR assay. Using commercial kits with optimised target regions and primer sequences (in the E gene and SARS-CoV-2-specific S gene) ruled out the unspecific signals completely. Hence, reasons for the observed unspecific signals may be dimerisation of primers and probes and/or unspecific primer binding and polymerase activity in the targeted region of the E gene, probably also depending on thermal profile and cycler-specific differences, or most likely a combination of these factors.