Processing of COVID-19 samples requires specialised biocontainment laboratories, operated by highly trained technicians, usually only found within medium-large hospital facilities. This has not only led to high false-negative rates, with probable cases remaining negative after multiple swabs, but is further exposing healthcare workers to risk of infection. Yet, SARS-CoV-2 loads in the respiratory tract have shown to vary considerably. Detecting SARS-CoV-2 from pharyngeal swabs requires high-quality specimens that contain a sufficient amount of intact viral RNA. However, RT-PCR diagnosis of COVID-19 has its limitations. And as only a very small amount of viral RNA needs to be present for amplification, these tests are highly sensitive in detecting virus from a sample. After taking a pharyngeal swab from the back of a patient’s throat, a sample can be sent to the lab to provide results within hours. The main advantage of RT-PCR has been its speed and sensitivity. Fortunately, thanks to rapid sequencing and publication of the SARS-CoV-2 genome in early January, RT-PCR primers and open access protocols were made quickly available, and are now being used by medical facilities worldwide to diagnose patients. The double-stranded section of DNA is then recognised and bound by a thermostable polymerase enzyme which acts as a molecular photocopier to extend the sequence and produce a full, complementary strand.īecause of this, diagnosing COVID-19 on the basis of clinical symptoms alone is highly inaccurate and must be confirmed by the use of highly specific diagnostic tests. PCR then begins by the addition of short DNA sequences known as primers, which bind the viral DNA strands. For patient diagnosis, a viral RNA or DNA sample is taken by swab or blood draw, before being sent to a specialist laboratory for analysis.įor RNA viruses, such as SARS-CoV-2, the polymerase chain reaction is preceded by an additional step to produce a complementary DNA template (cDNA) from RNA, by the addition of a reverse transcriptase enzyme (hence, Reverse Transcription-PCR (RT-PCR)). The polymerase chain reaction is a routine laboratory technique used to amplify small samples of DNA into larger quantities that can be detected and analysed. The two major methods for diagnosing viral infection are the polymerase chain reaction (PCR), and immunoassays:
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