Thread by @kevinpurcell

UW Virology Lab posts a preprint of “comparative review” of seven primer/probe RT-PCR tests.

Comparative Performance of SARS-CoV-2 Detection Assays using Seven Different Primer/Probe Sets and One Assay Kit

Spoiler alert: they all worked 😀 medrxiv.org/content/10.110…

“We report here our observations comparing three different RNA extraction methods.”

“We also compare the performance of SARS-CoV-2 detection assays using seven different primer/probe sets and one assay kit.”

Seven primer/probe sets:

University of Washington (UW) RdRp primer/probe set

Corman N-gene, RdRp, and E-gene primer/probe sets.

Centers for Disease Control (CDC) N1, 91 N2, and N3 sets

Assay

The BGI RT-PCR detection kit (BGI)

“Assays using UW RdRp and Corman N-gene primer/probe sets found to have LODs of 1:2x10e3”

I.e. the positive clinical sample was diluted by a bit more than 1000 times to give an undetectable sample.

“Assays using the Corman RdRp and E-gene sets found to have LODs of 1:2x10e4”

Ten times more sensitive than the UW RdRp and Corman N-gene primer/probe sets.

“Assays using the CDC N1 and N2 primer/probe sets performed better those using the N3 set”

“Assays using the CDC N2 and Corman E-gene primer/probe sets were more sensitive than those using the CDC N1 and Corman RDRP sets and the BGI kit”

“The least sensitive assays were the ones that used the Corman RdRp primer/probe set. At a dilution of 1:10e5, only 17 out of the 20 assays that used this set were positive for SARS-CoV-2.”

“The most sensitive assays used the CDC N2 and the Corman E-gene sets for which 18 and 17 replicate assays, respectively, were positive at a dilution of 1:10e6.”

“Assays using the CDC N1 and N2 sets and the BGI kit were found to be 100% specific.”

“The performance characteristics of assays using these primer/probe sets and testing kits are variable. Of the seven different primer/probe sets and one testing kit that we evaluated, all were found to be highly specific with no false positive results observed”

“we also show that it is possible to 194 significantly increase capacity for the RNA extraction step of SARS-CoV-2 testing without sacrificing 195 sensitivity”

This explains a comment UW virology made that they could reduce the amount of reagent need to extract RNA.