TESTING FOR THE coronavirus has been a key part of measures to track transmission and prevent the spread of the virus. 

With the government bringing the entire country under Level 3 restrictions from tonight, and health officials warning a move to Level 4 or even Level 5 is still on the horizon, the testing regime will have to be robust to drive down transmission.

There has been an increase in testing and the HSE has said it plans to increase capacity in Ireland to 100,000 per week. Additional lab capacity to expand on this 100,000 tests per week will continue to be available in Germany if required.

Some posts being shared on social media in recent weeks have claimed there has been a recent increase in Covid-19 cases in Ireland because there has been an increase in testing.

It is a familiar claim, frequently used by US President Donald Trump, who has regularly blamed the rate of testing in the US for surges in coronavirus cases. This was despite evidence that the virus was spreading widely through many communities.

We’ve looked at whether an increase in testing in Ireland results in an increase in the number of positive cases – it doesn’t – and whether increased testing skews data on transmission levels. 

Dr Cillian de Gascun, director of the National Virus Reference Laboratory, has said Ireland’s positivity rate – the percentage of people tested that week who receiveed a positive result – has increased from 2.9% last week to 3.9% this week. This is despite an increase in the level of testing. 

“The positivity rate has increased dramatically in the last few weeks,” he told TheJournal.ie.

“The positivity rate gives you an indication of transmission levels. Ideally we’d like to be testing more and for the positivity rate to either stay the same or decline because that means you’re chasing down the virus.”

Back at the end of March this year, some 30,213 tests had been carried out in laboratories across the country.

The positivity rate the week ending 31 March was 15%, having risen in one week from 6%.

This followed a change in the case definition, which restricted availability to patients with at least two symptoms and prioritised groups such as frontline healthcare workers, older people and those with an underlying condition. 

The test and trace system was under pressure and was unable to scale to the larger capacity we have now. 

In the first week of April, 12,271 tests were carried out in laboratories, with 2,347 positives and a positivity rate of 19%. 

Two weeks later, testing had scaled up to almost 21,000 tests a week with the positivity rate remaining at 19%. And between 20 April and 27 April more than 41,000 tests were carried out, resulting in a positivity rate of 12.9%.

In this case, doubling the amount of testing did not result in a doubling of positive case numbers week-on-week.

In the week 14-20 April, 3,907 positive cases were identified, compared to 3,996 the following week, when the level of testing doubled from 21,000 to 41,000 tests per week. 

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There has been growing concern in recent weeks about increasing case numbers across the country and in particular in certain counties such as Dublin, Donegal, Cork, Limerick and Galway. 

In the last couple of weeks 80,000 to 90,000 tests were completed per week. 

Dr de Gascun said it is true to say the testing system is picking up more asymptomatic cases now than it was in March and April, because the testing system back then was targeted towards those showing symptoms.

“At the very beginning of the pandemic, it was based on a history of travel and symptoms, then we moved the travel requirement and it was based on symptoms. At that stage we weren’t testing contacts of cases, which we are now. 

“We also hadn’t started the serial testing programme throughout the nursing home sector, direct provision or meat processing plants.”

“Obviously the more testing you do the more cases you’ll find, the reason for testing more is to identify those people who either don’t present for care for whatever reason – no access to healthcare or in a vulnerable group – or to identify people who don’t have symptoms and for that reason they wouldn’t present for care,” he said.

Since the middle of May, Ireland has been testing close contacts of confirmed cases on Day zero and again seven days later.

“That’s where we’re finding quite a lot of cases, in that close contacts of a confirmed case setting,” Dr de Gascun said. “And true to say we wouldn’t have picked all of those individuals up back in March and April.”

He said health officials want to “throw the net broadly” and if they are not finding a significant number of cases it can provide reassurance.

“Our concern now is that we are testing more and because the virus is widespread in the community our testing rate is increasing. As the positivity rate increases, the concern then arises that you may be missing cases.”

He said countries take different approaches in terms of their acceptable threshold for the positivity rate.

“I don’t have an exact figure for the threshold, some take it at 2 or 3% but some would allow it as high as 10%.”

Last week the HSE said the positivity rate in Ireland was 2.9% – this week it has risen to 3.9%. Serial testing in nursing homes, direct provision centres and meat processing plants also dilutes the overall national positivity rate. 

The positivity  rate in nursing homes last week was 0.17%, in direct provision centres it was 0.53% and in meat plants it was 0.32%. This indicates the positivity rate in the community is higher than the overall 3.9%.

More testing

This evening health officials confirmed 432 new cases of Covid-19 in Ireland, with new positive cases identified in almost every county. 48% of those were associated with outbreaks or were close contacts of a confirmed case. 60 of the 432 have been identified as community transmission. 

Dr de Gascun said the current positivity rate suggests “we probably need to be testing more”. 

“If we were in the position where everyone was 100% compliant with the public health measures we would probably be able to control this without testing more.

“But in the context of trying to monitor the epidemiology and spread, we would probably need to be testing more to drive that positivity rate back down and give us some confidence.”

Last week HSE CEO Pail Reid said the health service has “re-calibrated the mix” of testing capacity with 100,000 in Ireland per week and a capacity of 2,000 per day in German laboratories.

“It is a good buffer for us should we need to draw on it,” he said. 

Dr de Gascun said it would be worrying moving forward if the health service continued to increase testing and the positivity rate remained the same or increased. 

“If we increased to 120,000 test per week and the positivity rate didn’t change, you’d be very concerned because then you know a lot of infection out there isn’t being picked up with the 100,000 capacity. 

“It’s something the HSE continues to look at, there seems to have been some perception that once we got to 100,000 a week then everything stops, but that’s not case. The idea is to ensure we have sufficient capacity there for whatever testing is required.”