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Infectious Diseases

Invasive Group A Streptococcal Infections (iGAS)

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What is Group A Streptococcal (GAS) infection?  

Group A Streptococcus (GAS) are bacteria commonly found in the throat and on the skin. People can carry these bacteria and have no symptoms of illness. When they do cause illness, it can occur in one of 2 forms:

  • invasive GAS infection; or
  • non-invasive GAS infection. 

What is the difference between invasive and non-invasive GAS?  

Common non-invasive GAS infections include Strep throat, scarlet fever, impetigo, and ear infections. These infections are less severe and more contagious than invasive GAS infections.

Invasive GAS infections are more aggressive and may cause conditions like Streptococcal toxic shock syndrome and necrotizing fasciitis.

What are the symptoms of non-invasive and invasive GAS?

Early signs of non-invasive GAS infection may include sore throat, fever, rash or a skin infection.

If you develop symptoms see a health care provider immediately. They might draw blood or swab the infected area to see if you have a GAS infection.

Early signs of necrotizing fasciitis include fever, severe pain, swelling and redness of the affected area. Early signs of Streptococcal toxic shock syndrome may include low blood pressure and shock, dizziness, confusion, red rash, nausea, vomiting and abdominal pain. Progression is quick so any person with these symptoms should seek medical attention right away.

How is GAS spread?

GAS is spread by direct contact with secretions from the nose or throat of infected people, or from contact with an infected wound or sore on the skin.  Symptoms usually start 1 to 3 days after being exposed to the bacteria. Open mouth kissing (“French kissing”), mouth-to-mouth resuscitation, sexual intercourse and sharing needles may put you at greater risk of becoming infected. It is rarely spread by casual contact or by touching common surfaces or shared objects.

Who is most at risk of invasive GAS disease?  

Very few people will get an invasive infection.

People with conditions like cancer, diabetes and kidney disease are at a higher risk than the general public. Any breaks in the skin (e.g. cuts, wounds) or chicken pox may provide an opportunity for the bacteria to enter the body.

Can invasive GAS be treated?

Invasive GAS infections are treated with antibiotics. Sometimes hospitalization and surgery are also needed.

How do I protect myself and others? 

Wash your hands especially after coughing or sneezing and before preparing foods or eating. Coughs and sneezes should be covered. All wounds should be kept clean. Watch for signs of infection.  If you think your wound is infected, see your health care provider.

Do contacts require follow up or treatment?

Close contacts of someone with invasive GAS will be contacted by the health unit. They will be told to watch for symptoms of GAS and seek medical attention right away if symptoms develop. Some close contacts of cases of necrotizing fasciitis or Streptococcal toxic shock syndrome may need to take antibiotics.


For data on the incidence of invasive group A Streptococcus in Simcoe Muskoka and Ontario, please visit the IGAS page on the health unit’s HealthSTATS site

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