COVID-19 testing in New Brunswick below 'minimum' prior to new outbreak

The discovery of six new cases of COVID-19 in the Campbellton area over the last week may trigger increased testing for the virus throughout New Brunswick, which had been slowing noticeably in the province in recent days to the point of falling below "minimum" amounts it set for itself.

Yesterday, New Brunswick's chief medical officer of health suggested the province might have been doing "too much" testing in May because of the long stretches of no new cases being found in the province — something the current outbreak has undone.

"The tricky parts about testing have to do with if there really, really are not very many cases or no cases at all," said Dr. Jennifer Russell in explaining why testing in New Brunswick has recently fallen below its own minimum targets.

"You test too much, your positivity rate changes and that can affect your data," said Russell.

Positivity rates are the ratio of positive test results to negative results.  

Ratio below WHO recommendation

According to Raywat Deonandan, an epidemiologist and an associate professor at the University of Ottawa, the World Health Organization recommends the positivity rate for COVID-19 testing should be below 10 per cent — in other words there should be at least nine or more negative tests for every positive one.  

New Brunswick's positivity rate is below one per cent with just one case identified in every 175 people tested since the beginning of the pandemic.

It was not immediately clear what problem with New Brunswick's data would be caused by a positivity rate that low, or lower, to cause a reduction in testing, but the province's numbers have been falling.

According to Public Health Agency of Canada data, New Brunswick tested 1,899 people for COVID-19 in the most recent full week, ended May 27. That's a 22 per cent drop from two weeks earlier and it's several hundred below the "minimum" number of people the province was targeting to test earlier this month.

"We knew that in order to give Public Health advice on removing Public Health measures as we go through the phases we would have to maintain a minimum number of tests of between 2,300 and 2,500 (per week) so that's our goal for the minimum number of tests," Dr. Russell told reporters on May 15.

New Brunswick has not been meeting those minimum amounts even while other provinces with limited new case counts have kept their testing numbers up.

Prince Edward Island has the lowest positivity rate in Canada among provinces — one case for every 218 people tested so far. It has also not found a new case in more than a month.

Still, over the last week P.E.I. tested 993 people, according to the Public Health Agency of Canada, a per capita amount 2.4 times the number of people New Brunswick tested.

On Thursday, Dr. Heather Morrison, P.E.I.'s chief medical health officer, said testing on the Island is one of its key strategies to prevent an outbreak there.

"When we hear about the case in New Brunswick, it reminds us how important all those measures are  — the screening of health-care workers before they come to work, the personal protective equipment but also the testing we're able to do," said Morrison.

Deonandan said ongoing testing is useful, even in jurisdictions where new cases are rare.

"If the case load is low, then the testing capacity should be employed as proactive screening to detect asymptomatic cases that otherwise would not prevent themselves," said Deoandan.  

The province appeared to have COVID-19 under control after a long stretch of no new cases in 35 of 39 days between April and May, including one period of 16 straight days without a new case.

The three new cases revealed in the Campbellton area Thursday were the most in a single day in New Brunswick since April 9.