Determination of daily reproduction numbers of SARS-CoV2 based on death cases suggests more rapid initial spread in Italy and the United States

Armin Ensser; Klaus Ueberla

Linearity and dynamic range of the assay. In a typical kinetic PCR amplification for bulk HIV-1 copy numbers, using the ACH-2 standard (Fig. 3A) , sigmoidal amplification curves were observed between 20 and 1 million HIV-1 copies per reaction, for a dynamic range spanning 4.7 logs. When the decimal logarithm of the HIV-1 copy number was plotted against the threshold cycle number between these limits, a strongly linear relationship was observed (Fig. 3B) . The regression line usually has a y intercept near 40 cycles (the maximum cycle number per reaction) and a negative slope, close to Ϫ3 threshold cycles per 10-fold increase in analyte concentration. Saturation is observed at copy numbers higher than 1 million copies per well (10 7 cells/ml). No amplification curves were observed below the limit of detection-20 copies per well in this example (Fig. 3B )-or in no-template controls (data not shown).