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Pooled Testing: Staying Ahead of COVID-19

COVID-19 shows no sign of slowing down, and governments around the world are struggling with resources in order to identify new cases.

Today, patients with symptoms or exposure to confirmed cases are being swab tested to slow the spread of the virus. However, by using one test kit per patient, the number of people that can be tested depends on kit availability and is subject to the capacity of the laboratories. And in a raging pandemic, there simply aren’t enough test kits or sufficient test laboratory capacity.

That’s why more and more governments are looking into pooled testing. This is a strategy that combines samples from a group of people for a single lab test, in order to save both time and resources. But how does it work? And why is it a better alternative?

What is pooled testing?


The idea of pooled testing was first introduced during the Second World War by a Harvard professor in order to screen new military recruits for syphilis. By testing a larger group at the same time, they drastically conserved test capacity and reduced costs.

The concept is quite simple. When an infection rate is low, as COVID-19 currently is in Singapore, the likelihood is high that no one in a random group would be infected. This group, ranging from 2 to 50 people, will have their samples merged and hopefully be collectively tested negative.

However, if one or more individuals in the group were to be infected, the group would test positive. Everyone in this group would then have to be retested individually. If the first pooling group size is large enough, the second test can still be pooled, by dividing the people into smaller groups; and as before, the final re- test if needed singly done. While the process needing re-tests may be viewed as incurring both extra costs and time delays, this is not necessarily the case.

Firstly, though the cost will rise for groups tested positive, it still makes financial sense if such an occurrence is rare as the overall average cost per person remains below that of testing everyone singly. Secondly, all supposed delays are more than made up for with the multiple-folds reduction of congestion expected from lengthy queues in laboratories had the tests been done singly.

The case for pooled testing

In a medical crisis like COVID-19, high, mid and low infection rate sub-populations co-exist. It is imperative to be able to classify and identify the many sub-populations vividly, understand their characteristics, and devise targeted strategies optimal to each.

High-infection rate people include walk-in patients to medical facilities. Mid-infection rate people would be individuals often in close contact with many others daily. And low-infection rate people would generally be everyone else.

There are also several situations where seemingly healthy people ought to be sent for screening.

These people include essential healthcare staff and community cleaning workers, who mingle with the masses daily. Migrant service, manufacturing and construction workers, who live in less hygienic conditions and travel primarily to and from dormitories and workplaces. International business and casual travellers, who journey from country to country. The latter group have seen testing become a mandatory requirement for many border crossings, regardless of the traveller’s origin.

Additionally, some people should be put on customised periodic screening schedules, while others should be tested whenever they are involved in specific scenarios that increase chances of viral spread, such as mingling with sub-populations or greater people-to-people interactions. For example, when a person is tested positive, his family members and colleagues in addition to those contact traced should be pool tested.

With vaccines still in the early roll-out phase, countries that are slowly recovering and reopening their economies in the new normal need to remain vigilant. They cannot afford a situation where there is a need for swab tests to be carried out on hundreds of thousands as in the case of people attending business conventions and conferences. This is why test pooling appeals as a solution.

In May 2020, Singapore’s Ministry of Health (MOH) piloted pooled testing with staff from nursing homes, blending up to five patient samples in each test. According to Kenneth Mak, the institution’s Director of Medical Service, such testing can not only be used where prevalence is low, but can also be efficiently employed in higher-risk areas like foreign workers’ dormitories as well[2].

Will pooled testing spread?

Essentially a back-office process, accounts of pooled testing in use are generally not made public. But one can assume that sensible governments would promote and require its use.

The strategy is already implemented in Germany, Israel and South Africa[3].Both China, where COVID-19 was first reported, and the US, where it is most aggressively spreading, have reported approving and using pooled testing.

A more pressing reason to push for its wider use would be to address the urgent need in many countries to screen huge numbers of migrant workers living in large, densely-packed dormitories. For such cases, lockdowns may not be the right answer.

In Singapore’s case — where foreign workers living in dormitories make up the vast majority of local cases — pooled testing can be invaluable in managing infection outbreaks.

Staff providing medical cover need to learn how to effectively use pooled testing, both differentiated and targeted. They have to assess the infection risk level and provide this as crucial input with regards to each swab specimen taken.

With a good tracking database, the different scenarios can be analysed and pooled testing regimes may be tailored to fit and regularly adjusted with evolving circumstances.

This article is written by Professor Leong Thin Yin, Lecturer, Business Programme, School of Business (SBIZ).

Citations

[1] TODAY (JUL 2020) Singapore scientists develop Covid-19 test method that delivers results in 36 minutes

[2] Straits Times (JUL 2020) Pooled tests can be used in dorms, community

[3] TIME (JUL 2020) Here’s What You Need to Know About Pooled Testing for COVID-19 and How It Could Lead to Testing More People

Resources

[1] Singapore Government, Ministry of Health Situation Report

[2] Channel News Asia (AUG 2020) COVID-19 cases detected again in cleared migrant worker dorms, about 7,000 quarantined due to new infections

[3] Straits Times (JULY 2020) China requires negative Covid-19 tests for arriving air passengers

[4] The Conversation (JULY 2020) China requires negative Covid-19 tests for arriving air passengers

[5] Darius Lakdawalla & Erin Trish, 2020.Group testing for coronavirus – called pooled testing – could be the fastest and cheapest way to increase screening nationwide

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