The Public Health Agency of Canada has restored COVID-19 wastewater data for New Brunswick on the national COVID wastewater website, following a five-month "quality review" related to concerns about the accuracy of test results.

The agency's national microbiology laboratory "wanted to assess the batch-to-batch variability" and sensitivity of the testing cartridges used in New Brunswick's GeneXpert system — a polymerase chain reaction rapid-testing platform for infectious diseases, said spokesperson Anna Maddison.

"Different batches of cartridges … may have differences in performance and this can affect the test accuracy, sensitivity and specificity," she said in an emailed statement.

"Prior to publishing data from a different batch of cartridges, the [national microbiology laboratory] conducted a quality review to … ensure the cartridges were reporting accurate results."

Maddison did not respond to questions about what prompted the review, which started in April and included testing "contrived and authentic" wastewater samples and "assessing quality metrics."

But "there were no identified issues with the new test lot."

The lab "temporarily paused" publishing data for all 10 New Brunswick testing sites on the federal dashboard until Sept. 20, after the review was completed, "out of an abundance of caution."

Until late last Friday, no recent COVID-19 activity data for New Brunswick was available on the national COVID wastewater dashboard site. (Public Health Agency of Canada)

As of Tuesday's update, COVID activity in the province is high, based on the 10 sites that submit wastewater samples, representing 39.5 per cent of the population. Eight sites have a high viral activity level, Campbellton is listed as "moderate," and no data is available for St. Stephen, with its last sample taken on Aug. 11.

Across Canada, COVID activity is "moderate," according to the dashboard.

When asked whether the national lab has had to pause reporting COVID wastewater data or conduct quality reviews for other provinces or territories, Maddison noted reporting of Saint John data was paused for several months last year during a quality review over concerns of the accuracy of its data. Officials believed samples were being drawn from a treated area and that the reported values were "not reflective of the community burden."

"It is generally uncommon for the [national lab] to pause testing," she added.

New quality controls being established

No changes were made to New Brunswick's published data as a result of the review, said Maddison.

However, "additional quality controls are currently being established to allow for the efficient validation of new GeneXpert test lots without disruption to routine testing and reporting."

The Department of Health declined a request for an interview or more information. Spokesperson Katelin Dean said the COVID-19 wastewater surveillance dashboard "is the responsibility of the Public Health Agency of Canada. Questions about the dashboard should be directed to PHAC."

There were no disruptions to New Brunswick sampling during the quality review, said Maddison. The national lab continued to receive data from the province, which has now been made public.

In the Saint John situation, national lab and New Brunswick scientists worked with local wastewater treatment personnel "to revise and refine the technical approach" to Saint John testing "to find a method that is sensitive and specific to their sewage treatment processes," and that data was restored in September 2023, Maddison previously told CBC News.