THURSDAY, Dec. 16, 2021 (HealthDay News) — Along with being contaminated, there was also a basic design flaw in COVID-19 testing kits created by the U.S. Centers for Disease Control and Prevention early in the pandemic, a new agency review shows.

It was already known that the polymerase chain reaction kits were contaminated, but the CDC findings published online Dec. 15 in PLOS ONE are the first to note a design error that caused false positives.

The test was originally designed to detect three regions, or sequences, of the virus’s genetic material. The kits contain a set of primers, which bind to and make copies of the regions, and probes, which produce a fluorescent signal when these copies are made, indicating that genetic material from the virus is present. Importantly, the primers and probes need to bind to the virus’s genetic sequences and not to each other. In this case, one of the probes in the kit sometimes bound to one of the primers, producing the fluorescent signal and generating a false positive.

The investigation also confirmed that the kits had been contaminated with synthetic fragments of the virus’s genetic material. These synthetic sequences, which are often used to ensure that the tests are working properly, were manufactured at the same CDC lab where the test kits were being tested for quality. It is “likely” that the test kits were contaminated there, the agency concluded in its report.

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