What Is Pool Testing And How This Could Help India Increase The Number Of COVID-19 Tests

The number of COVID-19 cases has crossed 11,000 in India and is rapidly rising over the past few weeks. While it is a big number, the number of COVID-19 cases in India is much lesser than most of the countries around the world, which has better medical infrastructure.

Though it is a good thing that the number of people who are testing positive for the deadly infection is very low there is an argument that it is because we aren't testing enough. Since the outbreak began India has been only conducting COVID-19 tests on those who had returned from abroad and those who had come in contact with patients tested positive.

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This has since changed and the scope of those who can be tested for COVID-19 has been widened. As of April 14, a total of 2,44,893 samples from 2,29,426 individuals were tested in India. The US and Italy, countries that have among the highest reported cases, have conducted 13 times and about five times as many tests as India has. India¡¯s tests come to 161 tests per million population fewer than the 8,625 tests per million In the US and 17,333 in Italy.

Now with the number of cases spiking and the fear of community spread in some areas the Indian Council of Medical Research (ICMR) on Tuesday laid down the roadmap for pool testing that may be conducted in less-affected areas of the country. The process of pool testing involves putting five swab samples together and testing them using a single reverse transcription polymerase chain reaction (RT-PCR) test.

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Sounding a note of urgency, the apex health research body said the number of COVID-19 cases in India is rising exponentially and in view of this, it is critical to increasing the numbers of tests conducted by laboratories. It said sample pooling for real-time RT-PCR screening for coronavirus is only recommended in areas with a low prevalence of COVID-19.

"Positivity rate in cases is still low. Hence, it may help to use the pooled samples for screening. A pooled testing algorithm involves the PCR screening of a specimen pool comprising multiple individual patient specimens, followed by individual testing only if a pool screens positive,¡± the advisory said.

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"As all individual samples in a negative pool are regarded as negative, it results in substantial cost savings when a large proportion of pools tests negative," it said while strongly discouraging pooling of more than five samples, except in research mode. The objective is to increase the capacity of the laboratories to screen increased numbers of samples using molecular testing for COVID-19 for the purpose of surveillance, the ICMR said.

It said a feasibility study was conducted at DHR/ICMR Virus Research and Diagnostic Laboratory (VRDL) at King George's Medical University (KGMU) in Lucknow, where it has been demonstrated that "performing real-time PCR for COVID-19 by pooling five samples of TS/NS (200 ul/sample) is feasible when the prevalence rates of infection are low".

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According to the advisory, all individual samples in a negative pool should be regarded as negative. "Deconvoluted testing is recommended if any of the pools is positive. Pooling of more than five samples is not recommended to avoid the effect of dilution leading to false negatives," the advisory said. "The sample pooling for real-time RT-PCR screening for COVID-19 is only recommended in areas with low prevalence of COVID-19 (initially using a proxy of low positivity of 5 pc for COVID-19," the ICMR stressed.

"Preferable number of samples to be pooled is five, though more than two samples can be pooled, but considering higher possibility of missing positive samples with low viral load, it strongly discouraged to pool more than five samples, except in research mode," the advisory said.

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With the rise in coronavirus infections in India, the ICMR has taken into account the need to expeditiously expand COVID-19 testing facilities in all parts of the country and has initiated a proactive search of potential laboratories that could be enabled for coronavirus testing, a senior official said. The ICMR has already invited applications from all government and private medical colleges for establishing COVID-19 testing facilities.