WINNIPEG -- Using 90 samples from COVID-19 positive tests in Manitoba, researchers from Cadham Provincial Laboratory, University of Manitoba, and the National Microbiology Laboratory have concluded that COVID-19 may not be infectious after eight days of symptoms.

The study used the reverse transcription polymerase chain reaction (RT-PCR), the most common kind of lab test used to confirm the virus that causes COVID-19. 

The PCR test can only detect nucleic acid from the virus.

From the positive tests, researchers created new cell cultures to see if the virus could still grow. 

The study, which was published Friday in the peer-reviewed journal Clinical Infectious Diseases, found the 26 samples that were taken within eight days of symptom onset demonstrated viral growth, and those taken beyond that time frame did not.

Researchers stated in their conclusion that this suggests infectivity beyond eight days of symptoms may be low, but more studies using a larger sample size are needed.

In Manitoba, those required to self-isolate, like those diagnosed with COVID-19, or people returning from international or interprovincial travel, must do so for 14 days.

“More work will be needed to review the results of this study, and any larger studies that are conducted, before any policy changes can be made,” a provincial spokesperson told CTV News in a written statement.

The authors said the research could help inform care, prevention, and control, as well as public health.

The study’s lead author is Dr. Jared Bullard, associate medical director at Cadham Provincial Laboratory, and associate professor and section head of Pediatric Infectious Diseases at the University of Manitoba.