Cases of norovirus, the bug behind 60 per cent of cases of 'stomach flu' in humans, are on the rise in Canada again after a few quiet years during the COVID-19 pandemic.
Norovirus, also known as Norwalk virus, affects people of all ages and is typically most active between November and March. It is highly transmissible and common in Canada, so most people here will have experienced an infection at some point in their lives.
Although pandemic-related precautions such as physical distancing, masking and thorough hand hygiene have made outbreaks less common over the last few years, public health experts say the virus is making a comeback this winter.
According to Dr. Isaac Bogoch, an infectious diseases expert at Toronto's University Health Network, norovirus infection rates in Canada right now are typical for the average pre-pandemic winter.
"Throughout 2020, 2021, even parts of 2022, we had school closures, we had business closures, we had stay-at-home orders and we had tremendous attention to sanitation and hygiene," Bogoch told CTVNews.ca in a telephone interview on Thursday.
"But the world today appears to be very similar to pre-pandemic times. There's social gatherings, people are back at work, kids are back at school, people are travelling, and many of the infections that decreased in frequency during 2020 and 2021 have started to re-emerge again."
According to the National Collaborating Centre for Infectious Diseases (NCCID), norovirus is highly contagious and has been the leading cause of acute gastroenteritis outbreaks around the world since 2002.
Gastroenteritis is an inflammation of the stomach or intestines usually marked by vomiting and diarrhea, and norovirus is responsible for an estimated 685 million cases of acute gastroenteritis each year. Most people will contract norovirus five times in their lifetime, according to the NCCID.
"Unfortunately, it doesn't take a large exposure to be infected with this, and the other interesting thing about norovirus is that it's actually rather hardy," Bogoch said.
"It will remain on surfaces for some time, and can be resistant to heat, cold and even alcohol-based cleaning products."
The typical route of transmission for norovirus is through infected bodily fluids and contaminants like saliva, vomit or, most commonly, fecal matter.
According to Dr. Tony Mazzulli, infectious diseases specialist at Toronto's Sinai Health, outbreaks typically occur in crowded settings such as schools, hospitals, childcare facilities, nursing homes, cruise ships and passenger trains.
"Someone who comes into contact either with a sick person or the contaminated environment, it gets onto their hands or their food … and they pick it up," Mazzulli, told CTVNews.ca in a telephone interview on Thursday.
"Anywhere where they're in a sort of close contact, a closed environment, it's very easy to transmit."
Drinking water and foods such as oysters, prawns and many fruits and vegetables can also easily become contaminated with norovirus due to exposure to sewage, according to the NCCID.
The incubation period for norovirus is between 12 and 48 hours, but symptoms such as nausea and vomiting can appear as soon as 12 hours after exposure.
"Symptoms can start rather abruptly in the sense that people will have pretty profound nausea and vomiting," Bogoch said. "Diarrhea can be a part of that but it is very frequently significant nausea and vomiting, and people will feel really unwell for about a day or two before symptoms start to abate."
The severity of symptoms will vary from person to person, and some people infected with norovirus may be asymptomatic. Older adults, people with compromised immune systems and young children tend to experience the most severe symptoms.
Symptoms usually start to fade after 24 to 36 hours, but Bogoch warned people infected with norovirus can shed the virus in their stool for "days or even weeks" after they've recovered.
"And that's why it's challenging to get rid of," he said.
There is no specific treatment for a norovirus infection. Since most people infected with norovirus begin to recover on their own after one or two days, treatment typically focuses on easing symptoms and maintaining hydration.
People sick with norovirus should drink plenty of fluids, including oral re-hydration drinks containing electrolytes, to replace those lost from vomiting and diarrhea, Mazzulli said.
"The very young and the very old are the ones who suffer the most because they may not be mobile to get up and go get something to drink," he said.
"Certainly, anti-nausea medication can help control it, if you can keep it down, or use of suppositories. But it's mostly just symptomatic treatment and keeping up with fluids."
People who are severely dehydrated may need medical attention or even hospitalization.
If there's a norovirus outbreak in your home, workplace or school, it can be hard to avoid becoming infected. However, there are steps people can take to protect themselves and others.
"Wash your hands, wash your hands, wash your hands," Mazzulli said. "You never know what you've touched, what other people have touched, or what's contaminated. Be careful not to put your hands up into your mouth into your nose."
Bogoch said the best way to keep your hands clean in a norovirus outbreak is by scrubbing with soap and water.
"Soap and water is better than alcohol hand sanitizers for this particular virus," he said.
Bogoch and Mazzulli said anyone in a household infected with norovirus should stay home to avoid infecting others for at least 36 to 48 hours, and that high-contact surfaces in the home should be cleaned regularly with a bleach-based product.
"Meticulously clean surfaces," Mazzulli said. "Certainly use household bleach, wipe the surface down, leave it there for about five minutes and then you can wipe away the bleach. That is probably the best disinfectant."
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