In 2 weeks, this Alberta city went from just a few cases of COVID-19 to the province's biggest hotspot

As Alberta prepares to re-open sectors of the economy that have been closed for weeks, the experience of one small city in late April offers a reminder of just how quickly COVID-19 can spread.

Brooks, Alta., is about a two-hour drive east of Calgary. It's home to about 15,000 people and one of the country's largest slaughterhouses.

In mid-April, three employees of JBS Foods were diagnosed with the disease. By month's end, more than 300 workers had been diagnosed and nearly 900 total cases had been recorded throughout the city.

Chief medical officer of health Dr. Deena Hinshaw said this outbreak — and an earlier one linked to another slaughterhouse in High River, just south of Calgary — demonstrate "the remarkable ability of the virus to spread quickly."

• Scroll down to see an animated chart showing the speed of the outbreak

"That is why we are doing everything possible to identify and manage every outbreak, including those in High River and Brooks," Hinshaw said.

Much of the public attention has focused on the Cargill slaughterhouse in High River, where one worker died from the disease and more than 900 others were infected. Most have now recovered and the facility, which was temporarily shut down, is due to re-open Monday.

One JBS worker has also died, but the facility has continued to operate, albeit at a reduced pace.

'It seems to be spreading in the community'

Four deaths, in total, have been recorded in Brooks, where the speed of the outbreak caught many by surprise.

Brooks Mayor Barry Morishita said on April 21 the root cause of the outbreak was still under investigation, but it seemed to be spreading, largely, outside of the JBS facility.

"Primarily it seems to be spreading in the community, at homes and at social gatherings and that sort of thing," he said. "There's a lot of work being done to try and figure all of that out."

What is clear is just how quickly COVID-19 can spread.

In the span of two weeks, Brooks went from a blip on the disease map to the province's No. 1 hotspot.

Brooks is located in the local health zone of Newell, one of 132 geographic areas Alberta Health divides the province into, in order to monitor diseases and other health outcomes.

On April 17,  the Newell zone had just three active cases of the disease. By the next day, that had grown to 33. The next, 103.

And that was only the beginning.

The animated chart below shows the top 10 local health zones in Alberta for active cases of COVID-19 over the last two weeks of April. Use the play/pause button at the bottom left to start or stop the animation, or drag the slider to adjust the date displayed:

(Chart not displaying properly on your device? Click here for a standalone version.)

By April 30, there were 824 active cases in the Newell local health zone, 813 of them in Brooks, itself.

That represents 26 per cent of Alberta's total active cases, in a city that makes up 0.3 per cent of the province's population.

The outbreak has helped pushed Alberta's overall caseload upward in late April, just as other provinces' curves started to flatten.

Alberta 'relaunch' looms

In other parts of the province, however, the disease growth has slowed to a trickle, even as testing criteria expanded to include anyone with symptoms.

In the broad Edmonton Zone, which includes more than 1.4 million people in the the city and surrounding area, there's been an average of just six new cases per day for the past three weeks. The Central Zone, home to half a million people between Edmonton and Calgary, has seen numerous days with zero new cases.

The vast majority of the spread has come in the Calgary Zone, which includes High River, and the South Zone, which includes Brooks.

With all this in mind, Premier Jason Kenney announced on Thursday that, in May, the province plans to start "carefully and gradually lifting the restrictions imposed on our economy and our lives."

"While we continue to see new cases and expect to as long as the virus is around, we've achieved our primary goal of flattening the curve of infections to keep our health-care system from being overwhelmed," he said.

He put a caveat on that, however. Public health officials will continue to monitor the spread of the virus and the dates of the multi-stage re-opening plan could be subject to change if they see something they don't like in the numbers.

Hinshaw said "our fight is far from over" and "we will continue to need each other more than ever in the days ahead."

"We must continue to use common sense to protect each other and help prevent the spread," she said.

"Please continue to wash your hands frequently, stay home when sick, maintain physical distance, and look out for each other in the days and weeks ahead."