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Coronavirus outbreak: Types of COVID-19 tests dejargonised

With rapid antibody testing set to begin in hotspot areas of India, The New Indian Express explains the various kinds of tests for the coronavirus.

Published: 17th April 2020 01:30 AM  |   Last Updated: 17th April 2020 01:30 AM   |  A+A-

A doctor conducts a swab test (Photo | PTI)

Express News Service

What is the most common test for Covid-19?

The most popular and common test for Covid-19 is the Reverse Transcription Polymerase Chain Reaction tests — a very sensitive test that looks for the RNA of the virus in a sample. Health workers collect swabs from patients or suspected patients from the mouth or the nose. The RT-PCR method can even pick out one virus particle from the samples. At the start of the outbreak, most countries relied on RT-PCR tests as they can give quick results: labs take a minimum of five hours.

What is rapid antibody testing and has it started in India?

One type of rapid antibody testing uses blood samples of suspected patients to test for the presence of the Covid-19 virus. It looks for antibodies in the blood of people believed to have been infected. Antibodies are produced over days to weeks after infection with the virus. Another type of rapid testing helps to detect the presence of viral proteins (antigens) expressed by the Covid-19 virus in a sample from the respiratory tract of a person. The antigen detected are expressed only when the virus is actively replicating.

Such tests therefore are best used to identify acute or early infection. Rapid diagnostic serological kits are required for such tests but they can give the results within 25-30 minutes. These kits can be used at small clusters or in villages to find out the number of infections quickly, which is important in the present situation. Reports suggest that Maharashtra, Telangana, Andhra Pradesh and few other states made a request that they be allowed to conduct such tests. Following the request the Indian Council of Medical Research ICMR has permitted rapid antibody testing but it is yet start as rapid diagnostic tests have only just arrived from China.

What is RT PCR pool testing and which states are doing this?

In pool testing, more than one sample from suspected patients is mixed and tested for the Covid- 19 virus. In Uttar Pradesh, for instance, one of the states to begin pool testing, more than 10 samples are mixed and tested for Covid-19. If they test negative, it is concluded that all the 10 samples are negative. But if the test is positive, then all 10 persons are tested individually to find out who is carrying the virus.

Pool testing is meant to save the number of kits used. Its need was felt as the number of number of cases rose sharply. A feasibility study was conducted at the ICMR’s Virus Research & Diagnostic Laboratory at King George’s Medical University, Lucknow, and it was demonstrated that performing real-time PCR for Covid-19 by pooling five samples was feasible when the prevalence rate of infection is low. Andaman and Nicobar Islands was the first region in India to start pool testing followed by UP.

What is door to door screening and which states are doing this?

All cities and districts where Covid- 19 cases have been detected are required to send teams of healthcare workers in every household for health surveys in areas ranging from 3 km, 5 km, 10 km radius (depending on the number of cases) or in the whole area identified under the cluster containment strategy. The healthcare workers ask people whether anyone has a history of international travel or they are suffering from any influenza like illnesses. If people with symptoms are identified they can be further assessed and tested for Covid-19. Door to door screening has been implemented in all states where Covid-19 cases have been detected. As of now, there are 377 districts where Covid-19 cases have been identified.

What is the limitation of RT PCR test?

20RT-PCR is very accurate. But, once a patient has recovered, the virus is eliminated and this test can no longer tell if they had been infected before. Also, RTPCR tests take much longer.

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