Group swab Covid-19 tests do not return positives to people without the virus

10 November 2020
What was claimed

Five different people’s Covid-19 swab tests are being sent off in one vial, so one positive test will contaminate the other four, giving five positives.

Our verdict

There are currently some trials of pooling samples, meaning a few samples are tested together to save resources. If all come out negative, they don’t need to be re-tested, but if any are positive, individual samples are tested again.

“Well in 30yrs of being a nurse, never seen anything quite like this. Pooling of tests. 5 different people's swabs sent off in one vial. So one positive will contaminate the other 4, giving 5 positives. What the hell is going on? Total madness #CovidUK #covidtest”

Posts on Facebook and Twitter have claimed that the existence of grouped swab tests mean that negative Covid-19 test samples are being contaminated with positive ones, and people are therefore being told they have tested positive when they haven’t.

This is not the case. Grouping swabs for testing is a standard method to save time and testing resources. It’s called sample pooling.

In general this involves different people’s samples being tested together—if the group tests positive, all the individuals can be tested again separately. If the group tests negative, there is no need to test each one individually. This could be useful in scenarios like student households, where a positive test for one person in a defined group would mean they all needed to self-isolate. 

But this is not a major part of the UK’s testing strategy yet. At least two studies of sample pooling are being done in England with rapid PCR testing (which tests to see if the person currently has the SARS-CoV-2 virus, which causes Covid-19). One is a pilot study, and another is testing asymptomatic people. These studies will be reviewed by the government’s Technical Validation Group, which includes representatives from Public Health England and the Medicines and Healthcare products Regulatory Agency before being incorporated into the national testing strategy. 

The purpose of pooled testing is to increase testing capacity at times when the prevalence of Covid-19 is low. 

The Facebook post’s attached screenshot appears to be from a government website for registering Covid-19 swabs, and gives the options of “single swab tests” and “group swab tests” described as “More than one person’s swab is put into the same vial. You can put up to 5 swabs into one vial.”

There is no reason to believe this screenshot isn’t genuine, but pooled testing is not standard practise for Covid-19 PCR tests done in the UK.

This article is part of our work fact checking potentially false pictures, videos and stories on Facebook. You can read more about this—and find out how to report Facebook content—here. For the purposes of that scheme, we’ve rated this claim as partly false because pooled testing is being undertaken in some trials in the UK but it doesn’t contaminate samples—if the pooled samples test positive, individual samples are tested again.

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