What to know about RSV, a virus surging among young children in Canada

Children's hospitals in Canada are seeing an increase in cases of a common respiratory virus that, in rare cases, can lead to severe illness in infants.

Respiratory syncytial virus (RSV) causes infections of the lungs and respiratory tract. It can result in severe infection in some people, including babies under two and older adults with pre-existing conditions.

Cases of RSV dropped dramatically early in the pandemic, but spiked last fall and are now surging in many parts of the country, says Dr. Earl Rubin, director of the infectious diseases division at the Montreal Children's Hospital.

Rubin says that surge is part of the reason his hospital is struggling with long wait times and a shortage of beds.

"We are overwhelmed," he said. "We are experiencing in the pediatric hospitals what the adult hospitals were experiencing during the peak of COVID."

Rubin says the "triple threat" of the flu, new coronavirus variants and RSV is cause for concern. 

Here's a look at what's behind the increase in RSV cases.

What is RSV?

The virus generally leads to cold-like symptoms such as runny nose, cough and fever. It's the most common cause of lower respiratory tract illness in young children worldwide, and typically leads to outbreaks in Canada from late fall to early spring. 

While many infections are simple colds, children less than two years of age are at risk of severe disease such as bronchiolitis — a blockage of small airways in the lungs — or pneumonia and may be hospitalized.

"Almost all babies are infected by two years of age. It's very common … but some babies can get very sick with it," said Dr. Anna Banerji, an infectious disease specialist and associate professor at the University of Toronto's faculty of medicine. 

In its most recent update, the Public Health Agency of Canada reported a rise in RSV cases in many parts of the country, though Banerji says testing isn't widespread enough to get a complete picture. Hospitals in the United States have also reported an increase in cases.

Quebec's Ministry of Health reported a higher positivity rate than the national average. CHEO, an Ottawa children's hospital, said in a statement RSV cases were part of the reason it "just had its busiest September ever."

Why are cases rising now?

Both Banerji and Rubin say there were fewer RSV cases when public health measures were in place because of COVID-19, but there was a spike last autumn and again this year as young children were exposed to more people.

Many of those children don't have strong immunity because they weren't exposed previously and, similarly, their birth mothers might not have been exposed and passed immunity on either, Banerji said.

At his Montreal hospital, Rubin says he's also seeing some slightly older children, between age one and two, that are sicker than usual.

"They have no immunity, and if they have any predisposing conditions, whether it's asthma or allergies, that will predispose [them to RSV]," he said. 

How does it spread?

RSV is predominantly spread by aspirated droplets, says Rubin. He recommends hand washing and, for older children, ensuring they sneeze into their elbow and cover their mouth when they cough.

It can also spread through contact. "If you touch a contaminated surface and then rub your eye, pick your nose, you can infect yourself," he said. 

People infected are usually contagious for three to eight days. Babies and people with weakened immune systems, however, can spread RSV for longer. 

Who is most at risk and what can be done?

Those with pre-existing conditions, particularly those born prematurely, can be vulnerable to the most serious infections. 

Studies conducted by Banerji also suggest that Inuit infants in Canada's north are particularly at risk. 

"They have much higher rates of admission than almost any other population in the world," she said.

During RSV season, injections of an antibody-based medicine are sometimes prescribed to protect premature infants and other very vulnerable babies.

Banerji launched a petition — now with more than 200,000 signatures — calling on the Nunavut government to expand the use of that medicine to make it available to all babies in the territory.

More generally, doctors may also prescribe oral steroids or an inhaler to make breathing easier. In serious cases, patients in the hospital may get oxygen, a breathing tube or a ventilator.

"If a child needs to be admitted to the hospital, it's because their oxygen levels are low or they're having a really hard time breathing on their own and may need to be ventilated or they're not feeding well," Banerji said. 

At home, she said, parents can do their best to manage symptoms with fever medications, and ensure their baby is adequately hydrated.

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