CALGARY -- Sean Edgar was feeling a little sick when he first flew from London to Amsterdam earlier this month, but not enough to really stop him.

He went to soccer games, rode trains and enjoyed the nightlife of Europe, while nursing a cough and bit of a sore throat.

"I never really got all that sick," Edgar says.

But when he came home to Calgary he was still a little sick — and his travel history raised flags. A couple days later and his test came back positive for COVID-19.

"The symptoms can be so subtle that you can pass it on and not even know," he says. "That’s the thing I’m most concerned about because I wouldn’t have known that I had the sickness, I could have passed it on to so many people."

Edgar is a paramedic — and could have spread COVID-19 to vulnerable patients. Fortunately his diagnosis came before he had a chance.

Community spread still makes up a small minority of known cases in the province — just 33 or 419 — but health officials say there are many more unknown cases.

Craig Jenne is an infectious disease researcher at the University of Calgary. He says people need to stay focused on containing the spread.

"The individual risk is quite low, but to your community it’s not," Jenne says. "If it gets into a long-term care facility, if it gets into a cancer unit at the hospital, things get very very bad very very fast."

Of Alberta’s cases of community transmission, more than 10 came from a single gathering at a northwest home. Of the people in attendance, three were hospitalized and two were admitted to the ICU, where one is still fighting for his life.

Calgary makes up roughly 60 per cent of Alberta's known cases. The province says that's due to the number of international travellers landing at the Calgary International Airport.

The deep south of the city has 66 total, while the northwest has the densest cluster with 60 cases.

While known infection rates vary widely by region, given the mild symptoms shown by some, it’s safe to assume it’s everywhere and more widespread than the official numbers suggest.

Aggressive testing and early measures to limit large gatherings have helped. There’s still time to get it wrong, but so far Alberta has put itself in a position to avoid the worst.

Italy has been the hardest hit country so far with nearly 75,000 cases by Wednesday and 7,503 deaths. Doctors and nurses are practising battlefield medicine — deciding who gets access to limited lifesaving resources and who will likely die.

"We had our first case almost a month before Italy, and here we are coming up to their number of cases a full month later," Jenne says. "So we’ve added two months to this curve."

Italy hit 470 cases on Feb. 26, which was an increase of 147 cases over the previous day.

By adding time for the health-care system to absorb new cases, it not only saves lives in the short term, but gives researchers time to develop more effective treatments that could reduce the number of severe infections. It also brings them closer to an effective vaccine.