Context

With more than 21,000 deaths and over 4 lakh infected and still increasing, the world is racing to develop a cure to this pandemic, along with providing affordable testing kits for the populace. 

• In this regard, let’s have a look what exactly are the testing techniques being used to find whether a person is infected with novel coronavirus (SARS-CoV-2) or not?

About

• Coronaviruses are a type of virus. There are many different kinds, and some cause disease. A newly identified type has caused a recent outbreak of respiratory illness now called COVID-19.
• The virus that has caused the corona virus disease (COVID-19) is small. Each particle is just between 50–200 nanometres in diameter.
• This makes direct observation under a microscope difficult. Simply, the tests for COVID-19 is divided into two:
  • molecular assays

immunoassays

Is this coronavirus different from SARS?·    SARS stands for severe acute respiratory syndrome. In 2003, an outbreak of SARS started in China and spread to other countries before ending in 2004. The virus that causes COVID-19 is similar to the one that caused the 2003 SARS outbreak: both are types of corona viruses. Much is still unknown, but COVID-19 seems to spread faster than the 2003 SARS and also may cause less severe illness.

• series of tests in the hospital.
• The lab will acquire one of the following samples from you:
  • A swab test: The lab will take a special cotton swab and sample the inside of the throat or nose
  • A nasal aspirate: The lab will inject a saline solution into your nose, then remove the sample with gentle suction.
  • A tracheal aspirate: A thin, lighted tube called a bronchoscope goes into your lungs, where a sample will be collected.
  • A sputum test: Sputum is a variation of mucus from your lungs that can be coughed out or sampled from the nose with a swab.
  • A blood test: The collected sample will be analysed for the virus, either through a blanket test for all variants of the coronavirus (including regular flu) or through a specialised gene sequencing test that locates the marker for the novel coronavirus.
• Currently, molecular assays are being used. These can be manual or automated.
• When a person is suspected to be suffering from COVID-19, an oral swab is taken. Viral Ribonucleic Acid (RNA) is isolated from these swabs using a variety of chemicals.
• But as this amount is very small, it is impossible to figure out the pathogen directly from this sample. To increase the test material, the polymerase chain reaction technique (PCR) is used.
• The coronavirus is an RNA virus and to use the PCR technique in such a sample, an additional step of treating the sample with enzyme reverse transcriptase is needed.
• Once the RNA is converted to a complementary strand of Deoxyribonucleic Acid (DNA), this DNA can be replicated many times over, generally 40 times.
• During the replication process, other than primers (which are specific to the viral genetic material), enzymes and nucleotides, fluorescent probes are added. These fluorescent probes are released from each strand when the copying of the strand is complete and provide a visual signal.
• If the sample had the coronavirus RNA, replication would occur and the visual signal would be there.

Immunoassays: 

• Other than the PCR technique, rapid tests have been launched in the market. These are immunoassays, which can be manual or automated immunoassays and rapid diagnostic tests.
• These follow the same principle used in pregnancy tests. They identify the IgM and IgG antibodies developed against the SARS-CoV-2.
• For the test, whole blood, serum and plasma can be used and if antibodies are present in the sample, these bind to the antigen immobilised on the test strip and give a coloured reaction.
• Such test kits are easy to use, provides quick results and also are effective in identifying asymptomatic patients.
• There is a risk of getting false positives and results need to be confirmed using a more advanced test. Many such tests are available globally but not in India.