Despite six weeks of workplace closures, physical distancing and stay-at-home messages, people are still contracting COVID-19 in Ontario communities, and public health officials don't have a firm handle on why or how it's happening.

Roughly half of Ontario's new cases of the coronavirus are among residents and staff of long-term care homes, along with other front-line health workers. But for the remaining cases, the sources of infection are often unspecified.

Experts say more precise data could help public health officials focus efforts and resources more intensely on the largest sources of infections. It could also help guide government decisions about the least risky locations to reopen when first loosening emergency restrictions.

Key questions about community transmission remain unanswered. Is it happening in workplaces that have stayed open? Supermarkets where physical distancing measures are falling short? On sidewalks as people pass one another?

These are the kinds of questions that Ontario's Chief Medical Officer of Health Dr. David Williams wants answered too.

Ontario public health officials Dr. Babara Yaffe and Dr. David Williams deliver an update on COVID-19 in early March. (Evan Mitsui/CBC)

"Who's getting infected? What's the demographics of this group still getting infected? What are the locations?" Williams said Tuesday during his daily briefing when discussing the unknowns of community spread.

To provide more detailed analysis of the latest trends, Williams said he wants Ontario's 34 local public health units to collect more specific information about likely sources of transmission among new cases.

"The timeliness is critical," he said, adding that such data would provide "a better current metric of how are we doing, what's going on, and what's not working."

Dr. Allison McGeer, director of infection prevention and control at Sinai Health System in Toronto, says it would help to know more specifics about community transmission, but adds a caveat.

"Knowing more is not simple, and a lot of cases are asymptomatic, so tracking transmission chains is hard," McGeer said in an email to CBC News.

Two of Ontario's largest public health units, York Region and Toronto, provided data to CBC News that suggest infections contracted in the community make up no more than one-fifth of all cases to date.

In the Toronto Public Health Unit, residents and staff in institutions with outbreaks make up 37 per cent of cases tracked, according to figures from Dr. Vinita Dubey, associate medical officer of health.

Of the remainder:

Neither public health unit could provide a more precise breakdown of the nature of community transmission, such as whether the infections likely occurred in workplaces, at essential retail outlets, on transit or in public spaces.

The sources of community transmission are "exactly what we're going to be thinking about" as Toronto prepares to ease restrictions, said Dr Eileen de Villa, the city's medical officer of health.

"Understanding what the major risk factors are and where those risk factors are found will help us determine how best we can reopen in our city in a way that's safe and actually best protects the health of our public," de Villa said Tuesday.

Although the city has not publicly reported any instances of people spreading infections in public spaces, de Villa was critical of Torontonians for flocking to the lakeshore pedestrian and cycle paths over the weekend. She has also rejected calls to free up more space by closing streets to traffic, saying it runs the risk of encouraging people to congregate.

Williams acknowledged that he is troubled by the continued evidence of community spread, seen each day in new cases reported outside of long-term care and other institutional settings.

"If everybody's doing as they should be doing, then the numbers should be dropping fairly significantly," he said. "We're still dealing with some individuals who are not adhering strictly to the social distancing."

The rate of transmission in the community is "why we keep saying that we have to continue practising social distancing and self isolation," Premier Doug Ford said Tuesday.

"That's why we have to be so careful about opening up the economy. We're going to be very very careful."