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Pooling can help India optimize its testing strategy

The Andaman and Nicobar Islands, which has recorded 16 confirmed cases of the coronavirus disease so far, was the first to implement pooled testingPremium
The Andaman and Nicobar Islands, which has recorded 16 confirmed cases of the coronavirus disease so far, was the first to implement pooled testing

  • The ICMR advisory recommends pooled testing only in areas with a covid-19 prevalence of less than 5% and says that not more than five samples can be pooled
  • Pooled testing involves putting multiple swab samples collected from people who may have been exposed to the SARS-Cov2 virus

Pooled testing is being seen as an effective way to conduct covid-19 tests on more people while reducing the load on laboratories. The Indian Council of Medical Research (ICMR) has also recommended using it in low-prevalence areas. Mint analyses the pros and cons.

What is pooled testing and how is it done?

Pooled testing involves putting multiple swab samples collected from people who may have been exposed to the SARS-Cov2 virus, and testing all of them using one real-time polymerase chain reaction (RT-PCR) test kit. If this pool tests 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 mix has covid-19. Each of these samples is then tested separately to identify the infected individuals. This strategy is more efficient in low-infection areas. It can help track asymptomatic cases and, thus, check community transmission.

Graphic: Paras Jain/Mint
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Graphic: Paras Jain/Mint

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Will such a strategy yield results for India?

The ICMR advisory recommends pooled testing only in areas with a covid-19 prevalence of less than 5% and says that not more than five samples can be pooled. If too many samples are tested together, there is a possibility of missing positive samples if the viral load is very mild or low. Individual tests are always more accurate, but doctors and health experts say pooled testing is crucial for India, which has a large population and a shortage of healthcare and testing resources, and trained personnel. Such a strategy not only saves costs and testing kits, but also means that more people can be screened faster.

Where is pooled testing being done in the country?

The Andaman and Nicobar Islands, which has recorded 16 confirmed cases of the coronavirus disease so far, was the first to implement pooled testing in the country early this month to counter the shortage of RT-PCR testing kits. Uttar Pradesh followed suit in mid-April and, now, Haryana, too, has ramped up pooled testing.

Has it been successful in other countries?

Pooled testing has shown success in Germany and Israel. Researchers at the German Red Cross Blood Donor Service in Frankfurt and the Institute for Medical Virology at University Hospital Frankfurt under Goethe University developed this method. Germany, with the lowest death rate in Europe, increased testing from 40,000 a 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’s the risk in using this testing method?

Pooled testing can help increase the testing rate substantially. But may not be as accurate as testing each individual. It is important to identify hotspots and non-hotspots clearly before deciding where to roll out pooled testing. Pooled testing of influenza-like illness and severe acute respiratory infection will help get a fair idea of transmission in green zones, based on which zoning can be changed. Pooled testing should be part of a larger strategy based on granular data that will first help identify where it should be conducted.

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