Antigen swabs prove testing for the experts

The antigen test card which is on sale at Lidl stores. Picture: Gareth Chaney/Collins

To mask or not to mask was the first pandemic dilemma, then ventilation, and now a split over antigen tests has spilled from academia onto our social media feeds, not least after they went on sale in Lidl. So what should we do?

At present, these tests are most regularly used in the country's meat plants, where HSE teams offer them in parallel with PCR testing.

A swab goes deep into the nose and is placed on a chemical liquid which must be read usually within 20 minutes. In meat plants, testers use egg-timers set on long tables to monitor this.

The tests look for a specific viral antigen and are most effective when people have a high viral load and are infectious. As they are less effective in the early stages of infection, regular testing is recommended.

The Health Information and Quality Authority (Hiqa) has said that, used like this at meat plants, the tests are effective.

However, chief scientist Conor Teljeur said feedback from the meat plants is not enthusiastic.

They found the tests time-consuming and finicky; even a tiny delay in checking makes the result invalid. Take-up is significantly lower than for PCR tests, said Dr Teljeur.

Tests at large events

The UK, with the benefit of 69.7% of adults on their first vaccine dose and 38.5% fully protected, is trialling antigen tests at large events.

However, spectators must have antigen tests “at a local testing centre”, not at home. They are also advised to take PCR tests before and afterwards.

“What we are doing here is case detection," Susan Hopkins, chief medical adviser to NHS Test and Trace, told the BBC before the events started.

"We are not saying people do not have the disease if their (antigen) test is negative.

“We are trying to say [to people testing positive], 'you do have the disease and now we want you to go and isolate for 10 days'."

Supporters of the tests get this nuance and assume we all do too.

Recommendations

In Ireland, the Ferguson report made 20 recommendations around the use of the tests despite a split among the authors, with some, including Mary Horgan, a consultant at Cork University Hospital, favouring a faster rollout.

Co-author Paddy Mallon posted online recently: “Visiting relatives today. No symptoms. Used approved #antigen test. Done correctly — read at 15mins. I am now at least 99.8% certain that I am not infectious today. Now I’m happier going to visit. That’s what the science tells me. Simple.” 

Maternity hospitals came under fire for not giving antigen tests to visitors, but the Rotunda’s Fergal Malone said simply he could not have confidence in a one-off test.

This echoes comments from public health experts.

If a workplace offers regular testing using a test approved for that setting, there is confidence that antigen tests will pick up asymptomatic cases.

There is less confidence that if we test ourselves on Wednesday before one event we will remember to do it again on Saturday. We need concrete advice around this.