"It's affecting everybody, our air quality health index is at its maximum category for risk in terms of health, both the at-risk population and the general population."

Before being diagnosed with COVID-19, Helmut Sieh used to walk 10 to 15 kilometres every day. Now, he struggles to step up and down the hallway in his condo complex with a rolling walker.

There's really no benefit to wearing them on your commute to work, and there may even be a downside, says the professor.

Muhammad Ali remained hospitalized Friday in the Phoenix area, battling respiratory problems serious enough to draw family members to his bedside.