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Rwandan researchers’ devise algorithm that can detect a Covid sample from pool of 99 swabs

Researchers from the University of Rwanda used the geometry of the hypercube to increase the accuracy of pooled Covid testing, making the test 20 times cheaper for individuals.

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New Delhi: Researchers from Rwanda have developed an algorithm for pooled testing of Covid-19 samples, which can identify even one positive case of the virus when mixed with 99 negative swabs.

This new mathematical approach can be used to screen large groups for the virus, which could prove to be 20 times cheaper than testing people individually.

The study, by researchers from University of Rwanda, was published on 21 October in the journal Nature and field trials of the algorithm are under way in Rwanda and South Africa. This method is also being used to screen air travellers in Rwanda and to test the rugby teams in South Africa.

According to the pooled testing method, samples of several people are collected in one tube. These are then put for screening through the RT-PCR test. If the pooled test turns out to be positive, each sample is tested individually.

However, if the pooled test is negative, then all the samples are recorded as negative. This helps to substantially reduce cost of testing samples.

Also read: ICMR recommends dropping Interferon, adding cancer drug Acalabrutinib to WHO Solidarity trial

Algorithm inspired by geometry of hypercube

The algorithm is inspired by the geometry of a hypercube — a cube with four dimensions —which can accurately identify infected patients with low viral prevalence in a small number of tests.

“Just one test suffices to show that no one is infected. Our algorithm takes full advantage of this powerful result,” the study noted.

“We have demonstrated its (algorithm) viability for group sizes upto 100, showing that cost savings of a factor of nearly 20 can, in principal, already be achieved,” it adds.

The researchers suggest that this algorithm could be used to test more people with a lower viral load at a cheaper cost. “This should incentivise decision-makers to act firmly to drive the prevalence down through massive testing, contact tracing and isolation.”

Also read: Ban on public events can bring down Covid transmission rate by 24%, Lancet study says

Rwanda’s Covid measures

Rwanda’s measures to contain the Covid-19 outbreak have been lauded by the World Health Organization (WHO) for ‘instituting a strong system’, which helped the country to ‘effectively confront’ the pandemic.

The country has made its Covid-19 testing voluntary and free. It has also employed a robust contact-tracing system to trace every possible case of Covid-19.

Rwanda has also been using the pooled-testing method for a while. They have been using 20 to 25 swabs in one testing sample so far. This algorithm is likely to make this method more effective now.

The country has recorded 5,017 cases of Covid-19 and 34 deaths so far.

Pooled testing in India

An advisory by the Indian Council of Medical Research (ICMR) published in April suggests that the preferable number of pooled samples in the country is five, as opposed to 100 samples suggested in this study.

The advisory states: “Number of Covid-19 cases in India is rising exponentially. In view of this, it is critical to increase the number of tests conducted by laboratories. Positivity rate in cases is still low. Hence, it may help to use the pooled samples for screening.”

Also read: Here is why the ICMR study that found plasma therapy ineffective on Covid is being questioned


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