The flu season is only just beginning, but almost 1,000 cases have already been confirmed in the Calgary health area, which is the most in the province – by far.
The Calgary area accounted for 65% of the total flu cases in Alberta, despite having only 38% of the population.
It was a similar story around this time last year when most of Alberta's flu cases were also recorded in the Calgary area.
But the rest of the province has recovered, and by the end of last season, the flu rate in Calgary was on par with the provincial average.
Influenza, by its very nature, is a complicated and unpredictable virus – or, more precisely, a family of viruses. So it's not clear exactly why Calgary is once again being hit, so soon.
But Dr. Eddy Lang has a hypothesis.
"The most likely explanation I heard is that because Calgary is seeing more international air traffic than in previous years, perhaps we are seeing more people coming into town already carrying the flu virus," said Lang, who is responsible for emergency medicine for adults in the Calgary area.
Calgary saw more than 1.7 million international travelers pass through its airport last year, compared to less than half a million in Edmonton, according to data from each airport authority.
"That's the only possible thing that, I think, would distinguish a previous peak in Calgary than in Edmonton, which has similar populations, similar demographics," Lang said. "I can not see it, unless it's a coincidence, because the flu would be more lush here than in Edmonton."
He said that emergency rooms in Calgary have had a recent increase in flu cases, with their "unmistakable" symptoms that set it apart from other illnesses such as the common cold.
Flu symptoms include high fever and severe muscle pain, Lang said, and patients often find themselves so fatigued that they can not get out of bed for several days.
So far this year, 200 people have been hospitalized in Calgary for laboratory-confirmed cases of influenza. That's four times the number in Edmonton.
The only flu-related death so far this year has also come in the Calgary area.
But medical doctor Jia Hu, a Calgary-area doctor, is not convinced that air travel is to blame.
Flu numbers over the years
"I think this is potentially a hypothesis explaining why this is the case," Hu said. "But again, I think the flu itself is more likely to be relatively unpredictable."
The initial rise in flu numbers over the past two years may simply be a coincidence, Hu said, noting that Calgary had fewer cases of flu in previous years.
In 2015/16, for example, the Calgary area had the lowest influenza rate in the province.
Click or tap the interactive chart below to see influenza rates by health zone in recent years.
Can not see the chart? Click here for a version that should work in your browser.
Regardless of the exact reasons, Hu said one thing is clear.
"The result is that we have seen a rapid increase in the number of flu cases in the Calgary area, which is why it is so important that people are immunized," he said.
Free flu shots are now available at clinics all over the city.
You can go to the clinic closest to you on this Alberta Health Services website.