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Cases of invasive group A strep are rising across the country. Here's what you need to know

Canada is seeing a record number of cases of invasive group A strep, a bacterial infection that kills roughly one in 10 people who contract it. Here’s everything you need to know including common symptoms, treatment, and who’s most at risk.

What is invasive group A strep and why is it dangerous?

A petri dish in the palm of someones hand.
Someone with invasive group A strep will be very, very ill, according to Dr. Donald Vinh, an infectious disease specialist at Montreal's McGill University Health Centre.  (Craig Chivers/CBC)

Canada is experiencing a record number of cases of dangerous, fast-moving strep infections.

Invasive group A strep, or iGAS, is a bacterial infection that can lead to serious, life-threatening complications. Provinces have also reported dozens of deaths in just the last few months, including at least 10 children across Ontario and in B.C. 

The latest tally of 4,600 iGAS samples processed for 2023 suggests the infection rate could now be as high as 12 cases per 100,000 people. 

Here's a look at common symptoms, when to seek medical attention, and who is most at risk.

What is invasive strep A?

Group A Streptococcus is a family of bacteria that causes mild illnesses, such as strep throat or skin infections.

John McCormick, a professor of microbiology and immunology at the University of Western Ontario, explains that there are non-sterile sites in our body where bacteria can exist without major concern.

In rare cases, the bacteria can move into a sterile site, such as into blood, soft tissue or underneath the skin. That's when the more dangerous invasive infection occurs. Group A strep bacteria in those places can lead to toxic shock syndrome, necrotizing fasciitis (flesh-eating disease), meningitis (inflammation around the brain) and sepsis (a blood-borne infection). 

How do you know if you have it?

Both forms of a group A strep infection share symptoms such as redness, pain and fever. But someone with invasive group A strep will be very, very ill, according to Dr. Donald Vinh, an infectious disease specialist at Montreal's McGill University Health Centre. 

"What we do know is that when people come to the hospital and they have [iGAS], they tend to be quite sick," said Vinh. "As a general rule, if you're well or, you know, well enough to do your normal activities, you don't usually have iGAS."

Keep a watch for symptoms like a lack of mental awareness, trouble breathing or chest pains, nausea, light-headedness and low blood pressure, he said.

Acetaminophen is normally effective in bringing down a fever from a group A strep infection. "If it doesn't, that's a worrisome sign," said Dr. Brian Conway, medical director of the Vancouver Infectious Diseases Centre. 

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Because iGAS can lead to many different complications, people should also be on the lookout for symptoms of necrotizing fasciitis, meningitis and sepsis. 

Necrotizing fasciitis can cause extreme pain and fast-spreading redness in specific spots on the body. Symptoms of meningitis include a severe headache, stiff neck, vomiting, sensitivity to light, and confusion. Sepsis can cause a fever or low body temperature, difficulty breathing, clammy or sweaty skin, and extreme pain. 

Experiencing any of these is a reason to seek medical attention, said Vinh. 

If you are unsure, most provinces have an 811 health information line, which will connect you to a registered nurse, said Conway. These phone lines are in service around the clock. 

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How can I get tested?

Having strep throat does not mean you will definitely develop iGAS — and you can develop iGAS without having had strep throat, said Vinh.

"It's not on a continuous spectrum. We think that these are different syndromes caused by the same bacteria."

Nevertheless, you should still get tested and treated for strep throat, said Vinh, as there are complications that could arise. Rapid tests for strep throat can be performed at many doctors' offices and even some pharmacies.

McCormick also said people should be getting strep throat checked, noting that an invasive infection can move rapidly.

But, he added, "it's a rare type of thing so the general population shouldn't be super worried." 

There is no test available to the public to diagnose iGAS. 

It is diagnosed by finding group A strep in a bodily sample where you normally wouldn't find bacteria, said Vinh.

"For example, it will take samples of your blood or samples of fluid around your lung," he said. These tests would need to be conducted in a hospital.

How is it treated?

An iGAS infection is treated with high doses of intravenous antibiotics. 

In the case of severe complications, such as sepsis or necrotizing fasciitis, surgery and amputation might be necessary.

Conway said that cases of severe sepsis would require a patient to be admitted to the ICU. "There can be damaged organs, such as your kidneys, that may not be completely reversible."

Who is at risk?

One study has found that the flu or chickenpox precedes iGAS in about 15 per cent of cases.

"Prior viral infections can predispose people to get invasive disease," said McCormick, "the big one is really chickenpox."

He said children who develop chickenpox, which is a viral infection, are much more susceptible to developing streptococcal disease. This is because chickenpox creates skin lesions, which then create portals for bacteria to enter.

Conway said that anyone with a weakened immune system, "especially if they have underlying heart or lung disease," is at risk.

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There is currently no vaccine for strep A but it is recommended to get your flu, COVID-19 and chickenpox (varicella) vaccines, said Vinh.

"If we prevent that upstream event, we think that we prevent afterward or decrease the risk for invasive group A strep."


Anna Spencer is a News & Current Affairs intern with the Health, Science, and Climate Change units. She previously interned at TVO on The Agenda.