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Pooled testing is considered an effective way to test covid-19 on more people while reducing the burden on labs. The Indian Council of Medical Research (ICMR) has also recommended its use in areas of low prevalence. Mint discusses the pros and cons.
What are grouped tests and how are they done?
Pooled testing involves taking multiple swab samples collected from people who may have been exposed to the SARS-Cov2 virus, and analyzing them all using a real-time polymerase chain reaction (RT-PCR) test kit. If this group is negative, it is concluded that the entire group is covid-19 negative. If the bulk sample tests positive, it indicates that at least one person in the mixture has covid-19. Each of these samples is tested separately to identify infected people. This strategy is more efficient in areas of low infection. It can help track asymptomatic cases and thus verify community transmission.
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Will that strategy pay off for India?
The ICMR advisory recommends grouped tests only in areas with a covid-19 prevalence of less than 5% and says that no more than five samples can be pooled. If too many samples are analyzed together, there is a possibility that positive samples may be missing if the viral load is very low or low. Individual tests are always more accurate, but doctors and health experts say pooled tests are crucial for India, which has a large population and a shortage of health and testing resources and trained staff. Such a strategy not only saves costs and test kits, but also means that more people can be tested faster.
Where are the grouped tests carried out in the country?
The Andaman and Nicobar Islands, which have so far recorded 16 confirmed cases of coronavirus disease, were the first to implement pooled tests in the country earlier this month to counter the shortage of RT-PCR test kits. Uttar Pradesh did the same in mid-April, and now Haryana has also increased clustered testing.
Has it been successful in other countries?
Clustered tests have been successful in Germany and Israel. This method was developed by researchers from the German Red Cross Blood Donation Service in Frankfurt and the Institute of Medical Virology at the University Hospital of Frankfurt at Goethe University. Germany, with the lowest death rate in Europe, increased the tests from 40,000 per day to between 200,000 and 400,000 without sacrificing accuracy. Researchers at Stanford University used it to track the early spread of the virus in the San Francisco Bay area.
What is the risk when using this test method?
Pooled tests can help to substantially increase the test rate. But it may not be as accurate as testing each individual. It is important to clearly identify critical and non-critical points before deciding where to implement grouped testing. Pooled tests for influenza-like illness and severe acute respiratory infection will help to get a fair idea of transmission in green areas, depending on which zoning can be changed. Pooled testing should be part of a broader granular data-based strategy that will first help identify where to perform.
