AHS apologizes after false-positive COVID-19 test at Edmonton hospital

Alberta Health Services is lifting outbreak protocols put in place Saturday at Edmonton's Royal Alexandra Hospital after a false-positive COVID-19 test led to the cancellation of some surgeries and placed the facility on alert.

In a statement to CBC News, AHS said the hospital had been dealing with potential exposure on two units from a patient who initially tested positive for the virus on Saturday.

Outbreak protocols were implemented the same day.

All patients on the affected wards were being tested, contact tracing was being done, some surgeries were cancelled and visitors to the hospital were restricted — until a retest on Monday revealed the patient was not actually infected.

"Two units at the Royal Alexandra Hospital are no longer under outbreak protocol after the one patient who was presumed to be COVID-19 positive, tested negative," AHS spokesperson Kerry Williamson said in an emailed statement to CBC News.

'We apologize'

"We apologize to anyone who was impacted by the postponement of their elective procedures, and we are working to have them rescheduled next week."

False results are uncommon, Williamson said. 

"Unfortunately, on very rare occasions, lab results produce a 'false positive.'"

"When rare errors do occur — and we are made aware of them — results are corrected, the root causes investigated, and corrective actions are taken to further mitigate the risk of such errors recurring." 

Following the false positive test, 13 hip and knee arthroplasty cases and three urogynecology procedures were cancelled.

Those patients will be rescheduled as high priority, as soon as possible, Williamson said.

All emergency and urgent procedures, as well as cancer cases, continued to be scheduled. An additional orthopedic trauma room had been opened to handle any new cases.

Health officials say testing is never 100 per cent accurate but the tests done at provincial labs exceed regulatory guidelines for accuracy and performance.  

"While we do not have a precise measure of the rates of false-negative and false-positive results, we anticipate these results to occur very rarely based on the evaluations that [Alberta Precision Laboratories] has carried out," Williamson said. 

There have been several high-profile examples of false-positive tests for COVID-19. A false positive in Nunavut's Pond Inlet came to light in early May and initially had government officials scrambling to get an emergency response team to the remote community.

A few days later, the territory's chief public health officer, Dr. Michael Patterson, revealed the the sample result "was re-tested, and deemed a false positive." The territory returned to zero confirmed cases.

False positives at long-term care facilities in Ontario — in Kingston, Lindsay and hard-hit Bobcaygeon — put local authorities on high alert last month, only to be ruled out as errors later on.

'A reverse lottery'

Health officials say all testing has limitations, and with an unprecedented number of tests being done in labs across Canada there is an increased risk of cross-contamination and automation error. 

Dr. Lynora Saxinger, an infectious diseases expert at the University of Alberta, said false-positives for COVID-19 are extremely rare.

With high number of tests being done every day, some anomalies are expected, she said. 

"We've only had this disease and its tests for some months but we've used tests similar to this for respiratory viruses for a long time and false positives are quite rare but not impossible," Saxinger said in an interview Tuesday. 

"This is like a reverse lottery type event, where unfortunately there will be the occasional very rare error." 

Across Canada, health workers use what's called "reverse-transcriptase polymerase chain reaction" (PCR) testing to confirm cases of COVID-19. In several places, they're also used to confirm when someone has recovered.

The tests evaluate a sample, taken with a swab of cells at the back of the nose and throat, for trace amounts of the coronavirus's RNA.

As of Tuesday, a total of  442,253 tests have been completed in Alberta.  

The testing is accurate and sensitive, Saxinger said but like all tests comes with limitations.  

There is a risk of cross contamination in the lab or in transport, Saxinger said. Another form of coronavirus infecting the patient could also lead to a false positive. 

"It tends to be a test that's very accurate and usually a well-collected test would be quite reliable but nothing is actually perfect. There's always a few per cent where the test might be inaccurate and it sounds like this might have been one of those." 

Saxinger said public health officials are more concerned about the possibility of false negatives, which usually result from the improper collection of swab samples.

"A false positive is probably preferred to a false negative, where you miss something that was there because then there might be transmission. 

"This just reminds us that it can go the other way too." 

Saxinger said Albertans should have faith in the testing protocols. In this instance, health officials acted quickly to slow possible transmission and were quick to detect the error. 

"It's always better to be safe than sorry with this, because clearly the consequences of the positive when someone who's been in hospital is a big deal and you have to take that very seriously.

"In a way, it means our systems are working the way that they're supposed to."