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Updated: Aug 25, 2025
Large-Scale SARS-CoV-2 Testing Utilizing Saliva and Transposition Sample Pooling
Published on: June 23, 2022
Patterns of Possible False-Positive Results for Three Commercial Real-Time PCR Kits for SARS-CoV-2
Background:
We retrospectively examined all initial positive SARS-CoV-2 test results using three real-time PCR tests from patients without a history of COVID-19 collected from September to October 2021 at a university-affiliated hospital.
Methods:
We defined a possible false-positive (PFP) case as a positive case that showed negative results upon per-forming a confirmatory test on the same specimen. Positivity% and PFP% were defined as the number of first positive and the number of PFP cases divided by the total test numbers, respectively.
Results:
The positivity%/PFP% values were 0.76%/0.10%, 0.29%/0.02%, and 0.21%/0.03% for the Xpert, Allplex, and cobas tests, respectively. Six (75%) cobas PFP cases were RdRp-only positive. All PFP cases analyzed by Xpert except one had cycle threshold values ≥ 40. Contamination during extraction was suspected in five of the 10 PFP cases analyzed by Allplex, which requires a separate extraction step.
Conclusions:
Care must be taken when analyzing first-positive cases as these may be false-positive signals.
