Would pool testing’ as a Covid-19 screening approach 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.

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.

Scope of pool-testing in Nepal

Can this approach be considered as an option 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.

Could it turn out to be a more cost effective method to quickly test the infection in community level?

“Pool testing is done to use less PCR test kit to conduct a large number of testing. If done properly it would save a lot of test kits,” explained Dr Anup Subedee, an Internist and Infectious Diseases Physician.

“It would have have been suitable if we had used this approach before the steep rise in infection in the country. However, using this method after the marginal increase in the number of infections will not save test kits but rather increase the workload for the relevant authorities.”

“As far as I know, Pool testing was once initiated in Nepal,” added Dr Anup. At that time, authorities had attempted this approach to test the infection in quarantine facilities. However, with a large number of infections detected at that time, the work got further complicated so it was abandoned.

Still, this approach can be used to detect infections in a certain community or location. It would not work in the areas with high infection rate rather should be used to rule out the probable infection in low-risk group or community, the doctor said.

The feasibility of pool testing in certain community in Nepal could be found out only after a detailed homework by National Public Health Laboratory.

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