Does ‘pool testing’ being considered as efficient Covid-19 screening make sense in Nepal?

KATHMANDU: US leadership is considering a new approach — pool testing — to efficiently include a large number of people for Covid-19 screening in the country.

The new approach is also known as batch testing in which swab samples are tested in batches instead of running them one by one.

The test-method is being considered by the United States health experts, including Dr Anthony Fauci, as an efficient approach for the US.

“Pooling would give us the capacity to go from a half-a-million tests per day to potentially 5 million individuals tested per day,” Dr Deborah Birx, the White House’s coronavirus response coordinator, told a recent meeting of laboratory experts.

In the pool testing, nasal swab samples of many people are taken and are mixed in a single tube. They are then tested together and the test will provide a single result for that grouping of samples.

The negative result would clear everyone in the batch while the positive result would require each sample to be individually retested.

Although the samples are mixed for the test, in theory, there should be enough initial samples for an individual test should it be needed.

According to US Food and drugs administration (FDA), as the samples are pooled together, ultimately fewer tests are run overall, meaning fewer testing supplies are used, and results can be returned to patients more quickly in most cases.

The FDA also cautions that as samples are diluted, which could result in less viral genetic material available to detect, there is a greater likelihood of false-negative results, particularly if not properly validated. This method works well when there is a low prevalence of cases, meaning more negative results are expected.

The theory of pooling was derived from World War II when batches of blood samples were tested to screen US army draftees for Syphilis. Later it was used to screen blood samples for HIV, Hepatitis, and Malaria.

China has been reported to have used pool testing in Wuhan, in a recent campaign to test all 11 million residents.

However, health experts say that pooling would not be the best option in the Covid-19 hot-spots and they recommend the approach when less than 10 per cent people are expected to test positive from the batch.

This test approach is likely to be one of the best options in Nepal as the country is struggling to stretch the testing capacity. Minister for Health and Population, Bhanu Bhakta Dhakal, on Tuesday said that six per cent of COVID-19 cases in Nepal have been detected in community level.

This level of transmission is well under the recommend level and the pool test is likely to make more sense than extensive Rapid diagnostic Test (RDT) being conducted in the country. It could also turn out to be a more cost effective method to quickly test the infection in community level. 

At a time, when the government is facing scrutiny and criticism for the lack of adequate PCR testing in the country, pool-tests are likely to create a breathing space for the authorities.

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