City and public health officials are warning young people to keep wearing masks and practise social distancing amid an increase in COVID-19 infections among teenagers and millennials.

“In the most recent two weeks, the average age of COVID-19 cases was 39 years old, compared to 52 years overall for the entire pandemic outbreak,” said Mayor John Tory, speaking at a COVID-19 update at city hall.

“The proportion of cases among those who are less than 19 years of age and those 20-29 years of age has increased significantly in the last few weeks.”

Tory said that while young people don’t typically suffer from the virus as much as older people do, they may live in inter-generational households with people who are more at risk. He said younger people are also more likely to work in the service industry, where they could potentially spread the disease to others.

“I know young people feel immortal and invincible — I can remember those days — but I urge them to be cautious and to keep following the public health advice because it applies to them, just as it applies to everyone else,” said Tory.

Dr. Vinita Dubey, associate medical officer of health, said the cases among younger people in the city seem to be arising from community spread.

“It’s probably because they’ve been in situations where they haven’t been able to maintain that physical distance, but it’s not necessarily that it’s pinned to any one gathering,” said Dubey.

She added that Health Canada’s COVID Alert app may help young people determine where they were infected and help prevent further spread of the virus.

The self-assessment app is available for free and encourages users to report whether or not they have symptoms, and to record their temperature if they can. It is available at Apple’s App Store and Google Play.

Tory said the city will be reaching out to young people through social media, including Tik Tok, a popular video-sharing service, but one that has raised serious privacy concerns.

Dubey said some of the proportionate increase in infections among young people is due to the fact that the number of older adults getting sick — in particular the elderly — is in decline.

The fact that fewer older people are being diagnosed is likely because there are fewer outbreaks in long-term care homes and retirement homes compared with earlier in the pandemic, Dubey said.

She said keeping the rate of infection low is crucial as children head back to school in September.

“We know if the cases are low in the community then there is less likely to be spread in schools.”

Francine Kopun is a Toronto-based reporter covering city hall and municipal politics for the Star. Follow her on Twitter: @KopunF