What is walking pneumonia, and why does it seem to be on the rise?

Mycoplasma pneumoniae, also known as walking pneumonia, is generally a mild bacterial infection that largely affects children and teens and can commonly be treated with antibiotics.

The infection got its informal name because people infected with it are generally not as ill as those with other types of pneumonia.

"It's called walking pneumonia because many people aren't sick enough to be flat out on their back at home or in a hospital," said Dr. Isaac Bogoch, an infectious diseases specialist at Toronto General Hospital.

"Many people can carry on about their daily routine feeling crummy but not sick enough to be staying at home. Having said that, that's just a colloquial term, and of course we know it can make some people very sick."

In October, the U.S. Centers for Disease Control and Prevention (CDC) reported a rise in cases of Mycoplasma pneumoniae infections, especially in young children. The increase started in the late spring, and case counts have remained high.

Canada does not track the number of cases of walking pneumonia, but anecdotally, doctors say they have seen an increase in cases.

Dr. Earl Rubin, a pediatric infectious diseases specialist at the Montreal Children's Hospital, said since the summer, he's seen patients being admitted to the hospital and testing positive.

"Speaking to colleagues across the country in pediatric infectious diseases, everybody is experiencing the same," Rubin said.

"We have received some signals of increased traffic in Quebec and are monitoring the situation," the province's Health Ministry said in a statement.

Halifax hospital IWK Health reported a total of 11 cases last year. So far this year, there have been 113 cases, including 28 pediatric inpatients.

The B.C. Centre for Disease Control said its surveillance indicates that the province is seeing more respiratory infections due to M. pneumoniae than in previous years — most notably among people under 20 — and it is monitoring the situation closely.

B.C. Children's Hospital in Vancouver also recorded an increase in children presenting with walking pneumonia at the emergency department since August.

The respiratory infection is caused by the bacteria Mycoplasma pneumoniae.

It spreads through the air, Bogoch said. This includes when a person coughs or sneezes, the CDC said.