Use pooled testing to identify hotspots, lower number of Covid-19 tests: CDDEP

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Published: April 5, 2020 5:30:55 AM

This will lower the number of tests to be conducted, while help identify corona hotspots faster, critical for any containment strategy.

India, too, has a had a low testing level so far—69,245 tests had been conducted till 9 pm on April 3, while 2,653 had tested positive.India, too, has a had a low testing level so far—69,245 tests had been conducted till 9 pm on April 3, while 2,653 had tested positive.

Even as India battles with inadequate supply of testing kits, researchers at the Center for Disease Dynamics, Economics and Policy (CDDEP) have advocated pooling of throat and nose swab samples in groups from a cluster like a housing colony, a neighbourhood or a slum for a more effective testing strategy. This will lower the number of tests to be conducted, while help identify corona hotspots faster, critical for any containment strategy.

“The use of a pooled testing strategy could reduce the time, cost and resources required, while identifying the infected people in a population and estimating the infection rate,” Ramanan Laxminarayan, study author and director, CDDEP, says. “The goal will not be to identify patients who are positive, but clusters. We can do this without having to test larger number of people at once.”

To illustrate, while one way to find out prevalence in a group of, say, 256 individuals, would be test each person individually, with pooled testing of 64 individuals, an average of just 7.3 tests would be required to identify a 5% prevalence.

Pooled testing has been done before, in the early years of HIV when PCR – a testing technique – was even more expensive. “Indeed, pooled testing was used in epidemiology even as far back as in the 1980s. The China-Cornell-Oxford project used this to determine average cholesterol levels amongst clusters,” says K Srinath Reddy of the Public Health Foundation of India.

Although the World Health Organisation (WHO) has stressed on wide Covid 19 testing as part of countries’ response to the pandemic, even most developed nations don’t have the capacity to execute this meaningfully—the public health authorities in the US, for instance, have been critcised for not testing widely enough in the initial days of the outbreak in the country. India, too, has a had a low testing level so far—69,245 tests had been conducted till 9 pm on April 3, while 2,653 had tested positive. Against South Korea’s 6,148 tests per million population (on March 20), India stood at 10.5 tests; this has risen since then, but not quite meaningfully.

Even as reagents and kits for upwards of 30 lakh tests are in the pipeline, Bloomberg reports that India’s 123 lakh public labs are operating at a 36% capacity while 49 private labs enlisted for testing managed just eight tests on average on Monday, all thanks to a lack of enough testing kits.

While pooled testing could be a solution to this and controlling Covid 19 spread, medical experts say there will be a concurrent need to ensure against false negatives and biosafety rigour to avoid likelihood of exposure to those dealing with multiple samples.

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