Dry Swab RT-PCR Covid-19 Test

• 28 Nov 2020

Why in News

Recently, the Council of Scientific and Industrial Research-Centre for Cellular and Molecular Biology (CSIR-CCMB) has got the permission of the Indian Council of Medical Research (ICMR) to commercially use the dry swab RNA-extraction free testing method for the Covid-19.

Key Points

• About:
  
  • Dry swab method has a consistency of 96.9%.
  • The comparison of conventional (swab-VTM-RNA extraction-RT-PCR) and the simplified (direct elution from dry swab-RT-qPCR) protocols suggested that dry swabs eluted directly into a simple buffered solution can support molecular detection of SARS-CoV-2 via endpoint RT-PCR without substantially compromising sensitivity.
• Conventional Method:
  
  • In the conventional testing method, nasopharyngeal or oropharyngeal swab samples are collected by sample collection centres from the suspected coronavirus patients. These are then transported to testing centres, sometimes even hundreds of kilometres away.
    
    • The nasopharynx is the upper part of the pharynx (throat) behind the nose.
    • The oropharynx is the middle part of the pharynx just beyond the mouth and includes the back part of the tongue (base of tongue), tonsils, soft palate (back part of the roof of the mouth), and the sides and walls of the throat.
  • The swab samples are generally placed in a liquid called Viral Transport Medium (VTM) and to avoid leakage, the samples are packed heavily that adds on to sample processing times at both the sample collection and testing centres.
  • RNA extraction, even with automation, takes four hours for roughly 500 samples. VTM and RNA extraction both add a significant burden on money and time required for mass testing.
• New and Simplified Method:
  
  • Dry swab technique does not require VTM and RNA extraction process, and can be directly used for RT-PCR testing.
  • It has the potential of bringing the costs and time of testing by 40-50% and the screening can also be enhanced several-fold with immediate effect while, at the same time, making the whole process safer.
  • It is easy to implement with no requirement of new kits and existing manpower can perform this with no additional training.
• Benefits:
  
  • It will scale up the testing.
  • More economical than conventional RT-PCR tests.
  • Quicker results

RT-PCR Test

• Kary Mullis, the American biochemist invented the PCR technique. He was awarded the Nobel Prize for Chemistry in 1993.
• Under the test, copies of a segment of DNA (deoxyribonucleic acid) are created using an enzyme called Polymerase.
  
  • The ‘chain reaction’ signifies how the DNA fragments are copied exponentially, where one is copied into two, the two are copied into four, and so on.
• A fluorescent DNA binding dye called the “probe” is added to DNA, which shows the presence of the virus on a fluorometer.
• Covid-19 is made of RNA (ribonucleic acid), so to detect it, RNA is converted into DNA using a technique called reverse transcription.
  
  • Then the copies of the DNA are then made and amplified.

Source: TH