Antigen testing in meat plants since March has reduced the risk of Covid-19 outbreaks and made them safer, the Department of Agriculture’s director of laboratories has said.
The department has been overseeing antigen testing of 4,000 workers in meat plants every week after a pilot in January found that the rapid antigen tests picked up about four out of five positive results confirmed by PCR tests, the standard and more sensitive test used by the HSE.
Dr Donal Sammin, assistant secretary of the department who is in charge of the testing programme, said antigen testing was "perfectly good enough" at preventing the spread of Covid-19 in meat plants where the circulation of chilled air encouraged the transmission of the virus.
He told The Irish Times that the antigen tests had allowed food businesses to pick out and remove workers most likely to transmit infection quickly from the factories before there was a chance of a “super-spreading event occurring in the plant”.
“It is not as sensitive as PCR, but it’s a good measure of infectivity. Our use of this test wasn’t so much to use it as an accurate diagnostic in individual workers; it was about using it as a risk-reduction tool in a population of people to make the workplace safer for all,” he said.
Long resisted by public health officials because of concerns about their accuracy, the general use of antigen tests is only now being given an enhanced role in the Government’s response to Covid-19.
In an effort to suppress the spread of the virus, the State will send antigen test kits to fully vaccinated asymptomatic people who are found to be close contacts of confirmed cases.
The Department of Agriculture found antigen testing to be effective in a validation study carried out on meat workers at the start of this year.
Tests on 5,111 workers in 17 meat plants in January compared antigen and PCR test results and found that 41 people tested positive on both tests.
Some 79 tested positive on the PCR tests but when the viral load was taken into account and those least likely to be infectious – or those who possibly had the virus previously and were no longer infectious – the antigen test picked up 79 per cent of positives confirmed by the PCR tests.
“When we look at those PCR positives, a rapid test is picking up four out of five of those so it is doing exactly what we would hope it would do,” said Dr Sammin. The sample found just two false positives out of the sample.
“One of the fears people have had about these rapid tests is that you might be getting a lot of false positives; that has not been our experience,” he said.
A key advantage of the antigen test is the result is available in 15 minutes whereas a PCR test typically takes two working days from a lab “which is too long to break transmission cycles”.