Bill walks into a coffee shop.

He has COVID-19 but does not know it. Bill sneezes on Anne, who walks past with her takeout coffee. If you were to test Anne for the virus the next day, or even a few days later, she would most likely test negative, even though she later developed symptoms and would most likely then test positive.

This is why health and government leaders are encouraging people to self-isolate as much as possible. You could have the virus and not know it.

And as Ontario, which has struggled to increase its testing capacity, finally does ramp it up in the coming weeks, the hypothetical story of Bill and Anne is a warning: a negative is not necessarily a negative.

“If a person is incubating COVID-19, but does not yet have symptoms, they will likely have a negative molecular test for COVID-19,” said Dr. Vanessa Allen, chief microbiologist at the Toronto lab. That negative result “might give false reassurance if they were tested.”

That’s why testing when a person has clear symptoms is more likely to determine if a person does or does not have the virus. As of Friday, the ministry of health reported that 92,673 people in Ontario had been tested for COVID-19, and 6,768 were positive for the virus.

While testing instructions are changing continually, the current provincial guidance is to test people with obvious symptoms — particularly if they are health-care workers or first responders — or people with no symptoms who are transferred from a hospital to a nursing or retirement home. In the latter case, the resident who is transferred would be isolated for 14 days and watched to see if any symptoms develop.

Ontario’s COVID-19 tests are done by Public Health Ontario, and a growing group of private and hospital laboratories.

The Star recently did a virtual tour of two floors of the provincial lab in Toronto (one of six provincial labs that conduct these tests), as new equipment arrived and capacity to test was raised in Ontario to 13,000 samples a day. Controversy in the provincial COVID-19 testing world continues as despite recent increased capacity, the number of daily swabs taken has dropped, though Premier Doug Ford said Saturday that situation will improve.

At the main provincial lab, technologists who perform the tests using high-tech machinery run the test in batches (usually 96 samples at a time) and upload the results to the Ontario Lab Information System. Positive results are telephoned out immediately to both the clinician who ordered the test and to the public health agency in the jurisdiction where the person lives.

The Star has found that one of the quirks of Ontario’s testing regimes is that people typically receive a negative result much later than they would receive a positive result because more resources are devoted to making sure the patient and public health knows of positive results.

A virus, unlike bacteria, needs human, animal or plant cells to thrive. When the outbreak began, the practice was to take two swabs from each potential case, one from the back of the throat and one from the nose. PHO’s Allen explains that the practice has changed to only taking a nose swab, which doubles the number of people who can be tested.

The machines that do the molecular testing for the virus are the size of a minivan. They take up a lot of space in a lab. Among the machines PHO has are two made by manufacturer Roche: one can run 4,000 tests a day, another can run 1,400 a day. The latter was just added last week.

Samples taken from the noses of Ontario residents are transported to labs in special containers that stabilize the material, even if it has to travel hundreds of kilometres from a testing site.

“You take the sample and you take out the genetic material. That process is called ‘extraction,’ ” says Allen. When she says “sample,” Allen is referring to what is on the nose swab. Part of the process involves stripping out contaminants so that the genetic marker of COVID-19 — if it is there — can be isolated.

(A previous tour of the lab in February is described by the Star’s Kate Allen, who breaks down the intricacies of the testing process.)

In addition to public health and hospital labs, big private labs including Dynacare and LifeLabs have been contracted by Ontario to run tests.

“Redundancy” is a buzzword that came up in the Star’s tour. The reagents — chemicals used to extract the genetic markers of COVID-19 — are prepared and packaged exclusively for one type of machine made by one manufacturer. Allen, who helps co-ordinate the response by all labs in the province, said one strategy Ontario is employing is to make sure they have several different machines.

If they were, for example, to run out of Roche reagents, the Roche machines would sit idle. But other machines, such as one made by Abbott, could continue to test with their reagents.

“To have a different method to do it. We are now buying different machines that have a different supply chain for the reagents. We have three different extraction machines right now,” said Allen.

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The type of molecular testing being done to determine if a sample is COVID-19 “is a very unique and expert skill,” says Allen. “It’s not a common expertise. A lot of microbiology technologists don’t have expertise in molecular microbiology. You can’t just say bring us all the technologists and they will be able to do it.”

Until the last two weeks, the provincial lab in Toronto was running two shifts. Now it has added a third shift and can test 24 hours a day. The Toronto lab, which used to be in an industrial area, now occupies the top four floors of the MaRS Centre in downtown Toronto.

Allen said because the nature of the testing work requires technologists to work in close quarters, a screening protocol is used at the main entrance of the lab. Any workers with symptoms or who believe they may have been in contact with a person with symptoms is not allowed into work. The lab is also practising “social distancing,” and food is provided so technologists do not have to leave the building during a shift.

“Like any other essential worker they are working in a tough environment and we are doing what we can to support them,” Allen said.