New Strains of Coronavirus Dodging RT-PCR Tests?

By SPS Pannu

The rising number of false negative tests for Covid-19, surfacing in the second wave of the pandemic sweeping across India, have become a cause for grave concern. This is being attributed to some new strains of coronavirus that the standard RT-PCR tests are not being able to detect.

There are increasing cases of patients with full-blown symptoms of Covid-19 testing negative. Health experts are of the view that the coronavirus is constantly mutating and some new strains have emerged which may not be detected by the current RT-PCR tests.

A false negative test report, leads to a costly delay in the treatment of patients and comes in the way of early isolation of infected people which is essential to prevent the rapid spread of Covid-19. It poses a major setback in the fight against the dreaded pandemic as such persons can turn out to be "super carriers" of the disease.

USFDA recommendations

The U.S. Food and Drug Administration (USFDA) regularly monitors the potential effects of genetic variation in molecular tests. It had alerted clinical laboratory staff and health care providers in the US in January this year that false negative results may occur with any molecular test for the detection of SARS-CoV-2 if a mutation occurs in the part of the virus' genome assessed by that test.

The FDA recommends clinical laboratory staff and health care providers who use molecular tests for the detection of SARS-CoV-2 to:

- Be aware that genetic variants of SARS-CoV-2 arise regularly and false negative test results can occur.

- Be aware that tests that use multiple genetic targets to determine a final result are less likely to be impacted by increased prevalence of genetic variants.

- Consider negative results in combination with clinical observations, patient history, and epidemiological information.

- Consider repeat testing with a different test (with different genetic targets) if Covid-19 is still suspected after receiving a negative test result.

The USFDA said it monitors these potential performance changes by comparing the sequence of genetic variants of the SARS-CoV-2 virus with the RNA sequences targeted by authorized SARS-CoV-2 tests.

The clinical impact of genetic variants on test sensitivity is influenced by the sequence of the variant, the design of test and the prevalence of the variant in the patient population.

Tests that rely on the detection of multiple regions of the genome may be less impacted by genetic variation in the SARS-CoV2 genome than tests that rely on detection of only a single region, according to USFDA.

Hasty testing also a factor

Another factor that has been identified for false negative test reports is the hasty manner in which some of these tests are being carried out. Prime Minister Narendra Modi had pointed out at the meeting with the chief ministers of states last week that they must ensure that tests are carried out properly.