FIG. 3.

Specificity test for N-gene-specific PCR. An amplification plot of fluorescence intensity versus the number of PCR cycles is shown. Black lines show the dynamic range of N-gene-specific PCR with a serially diluted plasmid construct (from 10¹ to 10⁶ copies). Results for NPA samples from non-SARS patients, including patients suffering from infections with adenovirus (n = 5), respiratory syncytial virus (n = 5), human metapneumovirus (n = 5), influenza A virus (n = 5), or influenza B virus (n = 5), are shown by gray lines. Triangles, SARS-CoV-positive NPA samples. NTC, no-template control. The x axis indicates the cycle number of the quantitative PCR, while the y axis represents the fluorescence intensity (FAM-490) over the background signal. The inset shows a melting curve analysis of the PCR products. Signals from positive (+ve) and negative (−ve) samples and from a no-template control are indicated.