The norovirus is spreading "at a higher pace" than expected in Canada, specifically in Ontario and Alberta, according to the Public Health Agency of Canada (PHAC).

Norovirus is a common, highly contagious virus that causes nausea, vomiting, abdominal pain, cramps, and diarrhea.

A spokesperson for PHAC told CTV News Toronto: “The number of reported norovirus cases was higher than expected in 2024 compared to the historical average for the past five years.”

PHAC specifically noted an increase in Ontario and Alberta, and to a lesser extent, in British Columbia, Saskatchewan, Manitoba, New Brunswick, and Newfoundland and Labrador.

The agency acknowledged that the historical five-year average the current rise is based on includes several years of the COVID-19 pandemic, a time when norovirus reports decreased.

Dr. Susy Hota, the head of infectious diseases for the university health network, stated that the pandemic is also a reason for seeing more cases.

Hota added: "People are doing more social things and going on cruises and types of exposure that carry risks for norovirus."

"I think we’re still going to see some changes in how common viruses behave because of the three years during which people were doing less and interacting less."

The Toronto Public Health (TPH) and Public Health Ontario (PHO) do not track norovirus infections. However, TPH surveys outbreaks, local increases in rates of infection or illness above what is expected in hospitals, long-term care homes, and retirement residences.

As of the latest report on Thursday, three outbreaks were reported in healthcare facilities in Toronto.

While we are seeing a slightly higher number of norovirus this year compared to previous years, Hota said: "There is nothing unusual at all, just more than we expect."

What is norovirus?

Norovirus, also known as the "Norwalk virus," named after the first outbreak that occurred in Norwalk, Ohio, causes diarrhea, vomiting, nausea, stomach pain, and cramping. Other symptoms include fever, chills, headache, body aches and muscle pain, and fatigue.

It is the most common cause of gastroenteritis, accounting for more than 60% of cases, according to the National Network for Infectious Diseases.

How does norovirus spread?

Norovirus is transmitted through contaminated surfaces and close contact with infected individuals, but it also has "hardiness," as Hota describes it, making the virus highly contagious.

It is difficult to eliminate the virus from surfaces because alcohol-based hand sanitizers are not effective in killing norovirus, as it can withstand relatively high levels of chlorine, making handwashing the best defense.

After becoming ill, symptoms may take between 12 to 48 hours to appear, which are usually at their worst during the first 48 to 72 hours, according to Hota.

She said: "The thing is, you remain contagious to others until about 48 hours after your stool returns to normal and diarrhea stops."

What to do if you contract norovirus?

There is no specific treatment for norovirus infection. Hota said: "Your body will take care of it." A healthcare provider can diagnose the virus by taking a stool or vomit sample for laboratory testing, according to the Primary Healthcare Center.

Hota added: "It’s unfortunate to go through those first forty-eight hours, but the important thing is to keep your body hydrated."

Medications for nausea can be taken to alleviate some symptoms, but she ultimately said that simply letting the infection "run its course" is the best way to go.