Canadian health officials are reporting a rising number of cases of the highly contagious norovirus illness in Canada, warning that the elderly and young children are most at risk.
Dr. Zain Chagla, infectious diseases specialist with St. Joseph’s Healthcare in Hamilton, Ont., says he’s currently seeing more cases of the “winter vomiting disease.”
“This is probably post-pandemic patterns that are just normalizing and (we’re) seeing across Canada and even the United States,” Chagla said in an interview with CTV Your Morning on Monday. “But this is the time we expect it.”
Norovirus, also known as the stomach flu or stomach bug, is a common gastrointestinal illness that occurs more often during the winter and early spring when people spend more time inside together, according to the BC Centre for Disease Control (BCCDC).
Norovirus symptoms
Symptoms include vomiting, diarrhea, stomach pains and nausea, according to the Public Health Agency of Canada (PHAC).
The disease normally spreads when people come in close contact with affected individuals or contaminated surfaces, it said.
People typically have symptoms lasting from 24 to 72 hours, according to the BCCDC.
Cases in Canada
Preliminary data indicate that a higher number of norovirus cases are being reported in recent weeks compared to the five-year historical average from 2019 to 2023, including in Alberta, Ontario, British Columbia, Nova Scotia, Saskatchewan and Prince Edward Island, according to PHAC in an email to CTVNews.ca on Thursday.
However, it cautioned that the comparison should take into account factors linked to the COVID-19 pandemic, which resulted in “significantly reduced reporting” of enteric pathogens like norovirus and lowered the five-year average over that period.
“As a result, recent trends may appear higher than expected when compared to the 2019-2023 reference period, but they do align with trends seen in the five year reference period preceding the pandemic (2015-2019),” it wrote.
PHAC said it can’t release any preliminary data until they are validated by provincial and territorial authorities.
Similarly, Alberta Health says cases have increased over the years, with 295 incidents in 2022, 513 in 2023 and 654 last year. However, it said no outbreaks were reported to the chief medical officer of health during that period, though they are common and can occur at any time throughout the year.
“Although Alberta has seen an increase in cases over the previous few weeks, which is not unusual to see … in the winter months, there are no confirmed outbreaks of norovirus in Alberta at this time,” according to Alberta’s Minister of Health’s office in an email to CTVNews.ca on Friday.
The BCCDC reports an “increasing amount of norovirus activity” in British Columbia, which it calls “typical” during this time of year.
“The levels of illness we’ve seen to date are elevated compared to previous years,” it said. However, it said data wasn’t immediately available.
Gastro-intestinal outbreaks, including those caused by norovirus, have increased in the past two years, according to Prince Edward Island’s Chief Public Health Office in an email to CTVNews.ca on Monday.
In 2023, there were 15 gastro-intestinal outbreaks, and in 2024 there were 26 outbreaks in the province.
Meanwhile, two long-term care homes in Saskatchewan are experiencing a norovirus outbreak, according to the Saskatchewan Health Authority in an email to CTVNews.ca on Friday. “While we do not have specific data immediately available, this is typical for this time of year.”
Treatment for norovirus
Experts say there is no treatment for norovirus, but those experiencing serious fluid loss are advised to seek medical care.
People should take small amounts of liquids, such as electrolytes-based solutions like Gatorade and Pedialyte, during the vomiting phase, which lasts about 24 hours, Chagla says.
“As long as people are generally healthy, as long as they get through that vomiting phase and as the vomiting settles down, they can start getting that hydration again, most people are able to tolerate the disease,” he said.
Preventing norovirus
Health experts say norovirus can spread through direct contact with contaminated food, water and surfaces.
They said hand sanitizer isn’t effective in preventing the virus, unlike soap and water. For disinfecting surfaces, bleach-based cleaning products are better, though they can be more toxic than regular products, so consumers should follow the instructions, Chagla added.
To avoid getting sick and spreading norovirus, practice good hygiene habits, such as washing your hands well with soap and water for at least 20 seconds after using the toilet, after changing diapers, and before eating, preparing or handling food, according to the U.S. Centers for Disease Control and Prevention (CDC).
Also, wash fruits and vegetables and cook shellfish thoroughly, it added, as well as clean and disinfect contaminated surfaces and wash laundry in hot water. If you’re sick, stay home for 48 hours after symptoms stop, it added.
Most people get better within one to three days, the CDC said.
Who is most vulnerable?
The disease can lead to dehydration and even death, with older adults and young children most at risk, according to health officials.
When is norovirus most contagious?
Norovirus is most contagious when people first start having diarrhea and vomiting, according to Chagla.
“The issue with norovirus is that it takes just as small as 15 viral particles – that’s a micro, microscopic amount of virus – to actually lead to someone being infected,” he told CTV Your Morning. “The worst is obviously when you’re having diarrhea and vomiting, which is filled with millions upon millions of viruses.”
People who have norovirus should “wash their hands aggressively” with soap and water and avoid high-risk environments where they could spread it even after they recover, as they could still be shedding viral particles, Chagla suggested.
With files from CTVNews.ca’s Jermaine Wilson