There was a steady flow of workers ascending the stairs to get swabbed for Covid-19 rapid antigen tests at Dawn Farm Foods, a production plant in Naas, Co Kildare, on Monday.

Since infections started increasing during this fourth wave, the company has moved from testing hundreds of employees once to twice weekly – every Monday and Thursday.

The aim of the screening programme, in place since March, is to catch possible cases of the disease before one infected person could cause a super-spreading event.

Hospital Report

"Having the antigen testing has just added another layer to feeling we have got a safety net here, that we we will quickly catch people if they just don't know they are unwell," says Nick Andrews, head of food safety and Covid defence with the company.

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With the latest wave of infection showing no sign of abating, despite high vaccination rates, the National Public Health Emergency Team and Government have been slowly embracing the use of antigen testing as another tool in the struggle against the virus.

Since last month, the Health Service Executive (HSE) has been sending antigen test kits to fully vaccinated, asymptomatic close contacts of virus cases. The Government is planning to extend rapid testing to schools and introduce a subsidy to encourage people to use them more generally.

The experience of antigen testing for food production firms and meat plants has been an effective one, even though they may not be as definitive a diagnostic tool as the PCR tests used in HSE centres.

“I am not trying to pretend that they are as sensitive, but in a practical setting . . . we have found them to be an extremely useful tool,” says Andrews.

Three testers from an outside healthcare company in personal protective equipment (PPE) come and take swabs from workers three times in the day to cover staff on three shifts. There are about 1,000 people working across the expansive facility, including Dawn’s 700 employees.

The facility is not a meat plant. It makes prepared foods such as pepperoni, chorizo, chicken strips and meatballs for food-supply businesses and restaurants.

Andrews says the company has picked up infections through antigen screening on a “very rare occasion”, with only “a fraction of a percentage of people” testing positive. He considers the programme “another layer of security” on top of other measures such as social distancing, wearing PPE and installing protective barriers and screens.

While public health officials have long been reluctant to embrace antigen testing – because they are seen as less sensitive than PCR testing – it has become a routine part of life at Dawn Farm Foods and and other food production facilities and meat processing plants.

Just over 100,000 tests were carried out across 42 meat plants and food production facilities between March and September under a programme overseen by the Department of Agriculture with test kits supplied by the HSE. Overall, 167 people were detected as having the virus.

“I am pretty certain that that would have prevented a larger outbreak occurring,” says Dónal Sammin, director of laboratories at the department, who oversees the programme.

Recirculation risk

Sammin considers antigen testing a “risk-reduction tool” in a high-risk setting like a food or meat plant, where the recirculation of cool air can result in easier transmission of the virus.

The less invasive nasal swabs used in antigen tests make them a more acceptable form of routine screening for staff. The gag reflex triggered by PCR swabs to the back of the throat can make it uncomfortable, especially if required twice weekly.

Sammin believes antigen tests are a better proxy than the PCR variety for detecting people who are more likely to infect others and spread the disease.

“If you get a signal on an antigen test, the likelihood is that you’re shedding significant amounts of virus, so you’re most likely to transmit it,” he says.

While Dawn Farm Foods use a professional contractor, other food companies use supervised self-sampling, which encourages staff to undergo testing.

Andrews says use of the contractor allows Dawn Farm to carry out a follow-up PCR test on the spot to confirm an antigen result. The result is then used to risk assess the worker – do they live with, travel to work or socialise with, other employees? They can then be isolated.

Had antigen testing been available last year, it could have prevented outbreaks across food plants in the summer that led to local lockdowns in Kildare, Laois and Offaly.

“What was difficult at the time was that there weren’t tools to really know where you were unless you went for a full PCR screening which is not easy to do,” says Andrews, who adds that antigen testing allows the company to “spot trends quite early on”.