VANCOUVER -- The rate of false-negative results in novel coronavirus tests can be as high as 30 per cent in some situations, B.C.'s top doctor says, which has shaped the way testing is done in the province.

During her Monday briefing where she announced 45 new cases of the virus, Dr. Bonnie Henry explained that when there's an outbreak of COVID-19 in a facility like a long-term care home, there's no point in conducting blanket tests of all residents.

"The testing, unfortunately, doesn't tell us the whole story. People can be negative one minute and positive within an hour. The test itself is not as sensitive as we expected it to be at the beginning," she said.

"We now know that the false-negative rate can be as high as 30 per cent early on in infection."

Instead, when an outbreak is identified in a facility, health-care workers are assessed and screened daily. Residents, on the other hand, might be screened several times a day for symptoms of the virus.

"The norm is not to test people who do not have symptoms because we know the test doesn't perform very well and we can have false negatives," she said.

"Having said that when we do have outbreaks, when we do recognize that people have symptoms in a care home, then we have a very low threshold for testing anybody to and make sure that we can try and get ahead of it as best as we can."

During Monday's briefing, Henry said 45 new cases of the virus were confirmed over the weekend and 11 more people had died.

The total number of people who have tested positive for the virus in B.C. is 1,490 and there are currently outbreaks in 20 long-term care homes.