Pooled testing to be used to help Government hit ‘moonshot’ target

It follows revelations by The Telegraph that manpower shortages have prompted health chiefs to appeal to untrained students to man the new Lighthouse laboratories in order to get England’s ailing testing system back on track.

Officials are also known to fear a potential global shortage of physical components, such as the crucial reagent solution into which swabs are dipped.

On Tuesday night, a Government source said: “Pooled testing is something we have been looking at, in theory testing batches of 10 to 50 at one time.”

The method is already being used in some parts of the NHS, including at North Devon District Hospital, where only samples from asymptomatic patients are being batched.

However, since the start of the coronavirus pandemic scientists in multiple countries have warned of false negatives, saying that combining too many samples risks reducing viral particles from an individual swab to such low levels that they may be undetectable.

Researchers in Germany have pooled as many as 30 samples but note that “borderline positive single samples might escape detection in large pools”. Scientists have also said pooled testing only works if the vast majority of results are negative.

Once too many composite samples come back positive, the time and cost demands of going back and testing individual samples can exacerbate rather than help backlogs, as well as getting through more precious chemicals.

Nebraska was a trailblazer for the technique in the US when it began combining five samples at a time in March. The initiative cut the number of tests by approximately half. But by the final week of April, when the positivity rate surged above 10 per cent, the scheme was abandoned as self-defeating.

The US Centres for Disease Control said pooled testing should not be used when positivity rates are above 10 per cent.

However, the world-leading Mayo Clinic believes pooled testing should be avoided when positivity rates exceed five per cent. That suggests batching swab samples from areas outbreak clusters would do more harm than good.

Positivity rates in England in the week to September 6 were 4.2 per cent (watch Boris Johnson announce his ambitions for the country’s testing programme in the video below).

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