What to know about 'devastating' invasive strep

Countries across the globe are reporting a sustained spike in the number of invasive Group A streptococcus (iGAS) infections at a time when the season for strep infections should be winding down, and Canada is among them.

iGAS is a potentially life-threatening infection involving the normally harmless Group A streptococcal bacteria (GAS). While GAS infection often causes mild illnesses such as tonsillitis, strep throat, scarlet fever and a skin infection called cellulitis, iGAS can cause severe illness and, in rare cases, death within days.

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Ontario and Quebec have reported higher iGAS infection rates during the 2022-2023 fall and winter strep season compared to pre-pandemic levels, and in Quebec, the infections have led to the deaths of several children and seniors.

Ontario reported 538 cases between October 2022 and February 2023, and Dr. David Fisman, a physician epidemiologist and professor of epidemiology at the University of Toronto, says some of those cases have been especially severe.

"This is an uncommon infection but when it does happen it can be devastating," Fisman told CTVNews.ca in an email on Wednesday. "Since Omicron emerged, we have seen a surge in iGAS in surveillance data, and also many of us who work clinically have seen weirdly severe iGAS."

According to the World Health Organization, countries including France, Ireland, the Netherlands, Sweden, the United Kingdom and the United States have also reported prolonged spikes in iGAS cases. In the U.K., 355 people across all age groups have died from infections this season.

WHAT IS iGAS?

GAS is a common bacteria that can only survive on and inside humans, explains John McCormick, professor of microbiology and immunology at the University of Western Ontario.

"It's the same bacteria that lots of kids carry around in their throats asymptomatically without showing any signs of disease."

Some people who carry GAS experience no symptoms, while others will become sick with symptoms such as sore throat, fever, headache and abdominal pain, but will recover on their own or with help from an antibiotic. Those types of symptoms occur when the bacteria is present in a part of the body that isn't considered sterile, like the throat or the surface of the skin. It's common for these parts of the body to be exposed to bacteria.

"So once you find (bacteria) in a location that should be sterile, then that's when they call it invasive. And this particular one, when it does that, can get to be very dangerous," McCormick said.

"If it gets into your blood, for example, or if it gets into the soft tissue, or even your muscle – that's necrotizing fasciitis or necrotising myositis – that's very rare but it does happen and it can be very dangerous."

Necrotizing fasciitis is also known as flesh-eating bacteria.

According to Dr. Anna Banerji, a pediatric infectious disease, tropical disease and global health specialist at the University of Toronto, a patient who survives iGAS could also face long-term health issues.

"There can be…post-strep complications that can affect the kidney and affect the heart," Banerji said.

WHY ARE NUMBERS SPIKING?

According to Banerji, it's probably not a coincidence iGAS infections spiked – along with respiratory viruses like RSV – after many countries lifted the public health restrictions put in place for COVID-19.

"This past year has been a very bad respiratory season, so strep A can be carried in the throat and not have a lot of symptoms, but when you have a cold, that allows the strep to invade," she said.

Like RSV, Banerji explained, many children avoided exposure to strep during the height of the pandemic and wouldn't have the antibodies needed to fight an infection now.

McCormick said there's another popular theory involving a handful of mutant strep A strains, including one named M1UK. M1UK was first discovered in the U.K. in 2019 and has been linked with spikes in scarlet fever and iGAS.

"It's got a mutation in it that means it makes a lot of a toxin…and that toxin, we know, could be involved in streptococcal toxic shock syndrome, which is a really dangerous form of the invasive disease."

McCormick doesn't know if M1UK or any other mutant strain of GAS has been linked to any of the cases of iGAS reported in Canada this year, but he knows some of the strains have made their way here. He's got samples in his lab.

"We know they're in Canada and the United States and other parts of Europe, and so that's probably contributing to the increase," he said.

WHAT DOES THIS MEAN FOR CANADIANS?

The rate of iGAS infections in Canada has been creeping upward since 2000, but infections remain uncommon, generally affecting fewer than 10 people per 100,000.

"I don't think people should be super worried, but I do think they should be aware of some of the symptoms," McCormick said.

Because GAS is so common and many carriers are asymptomatic, McCormick said it's difficult to avoid exposure. Aside from the usual public health best practices – such as practicing good hand hygiene, covering coughs and sneezes and staying home when you're sick – Canadians should know to intervene early when signs of a strep infection appear.

"If they have a child with a severe sore throat or a fever and maybe a rash, then they should go to their family physician and they'll likely be prescribed an antibiotic," he said.