The Bio-Rad SARS-CoV-2 ddPCR Test is a reverse transcription (RT) droplet digital polymerase chain reaction (ddPCR) test designed to detect RNA from SARS-CoV-2 in specimens (mainly nasopharyngeal, anterior nasal, oropharyngeal and mid-turbinate swab but also nasopharyngeal wash/aspirate and nasal aspirate specimens) collected from individuals who are suspected of COVID-19 infection.~This single assay multiplex test enables a one-well reaction with three sets of the oligonucleotide primers and probes which were reported by CDC. Two were selected from regions of the virus nucleocapsid (N) gene. An additional primer/probe included in the panel is set to detect the human RNase P gene (RP) in control samples and clinical specimens.~RNA isolated and purified from swab specimens is added to the mastermix comprised of reverse transcriptase whereby RNA is converted into cDNA and then amplified, using the Bio-Rad One-Step RT-ddPCR Advanced Kit for Probes.~Briefly, the sample and mastermix RT-ddPCR mixtures are fractionated into up to 20,000 nanoliter-sized droplets in the form of a water-in-oil emulsion. The 96-well RT-ddPCR ready plate containing droplets is sealed with foil using a plate sealer. The emulsions are then thermocycled to achieve reverse transcription to generate cDNA followed by target amplification plus probe hydrolysis in each droplet. After thermocycling is complete, the 96-well RT-ddPCR ready plate is loaded into the Droplet Reader. The Droplet Reader singulates the droplets and flows them past a two-color fluorescence detector (FAM and HEX) in order to determine which contain target (positive) and which do not (negative) for each of the targets identified with the SARS-CoV-2 ddPCR Test: N1, N2 and RP. The ddPCR system uses the QuantaSoft 1.7 and QuantaSoft Analysis Pro 1.0 for analysis software.
Evaluation of the ddPCR ability to detect the SARS-CoV-2 in nasopharyngeal samples of symptomatic patients with suspected COVID-19 infection using an IgG serological assay (EUROIMMUN Anti-SARS-Cov2 ELISA Ig) as gold/reference standard (FDA validated commercial serologic test).