Invasive Group A Streptococcal disease (iGAS)

Group A streptococci (GAS) - also known as Streptococcus pyogenes - is a bacterium (germ) commonly found in the throat and on the skin. People may carry GAS and have no symptoms of illness. Occasionally, the bacteria can infect the blood, muscle tissue or lungs and cause serious illness. This is known as invasive Group A Streptococcal disease (iGAS).

iGAS is a notifiable condition1

How GAS is spread

GAS bacteria (germs) are usually spread between people through coughing, sneezing, kissing, or direct skin-to-skin contact.

Both people who carry GAS and people who are unwell with a GAS infection can pass these bacteria on to others.

What is iGAS

Invasive GAS infection, or iGAS, may occur when GAS bacteria get into parts of the body where these bacteria are not usually found and cause a severe infection, such as infection of the blood, joints, or the birth canal after childbirth.

Although iGAS is uncommon, it is a very serious disease. The infection can develop very quickly and, depending on how the disease presents and progresses, can be fatal.

Signs and symptoms

Early signs and symptoms

Early signs and symptoms of iGAS may include:

  • fever
  • sore throat
  • skin rash or redness around a wound site
  • severe headache
  • shortness of breath
  • severe limb pain or muscle aches.

Severe signs and symptoms

iGAS can present with severe infection in various parts of the body:

  • Meningitis (inflammation of the lining of the brain and spinal cord) – symptoms  include fever, headache, irritability, drowsiness, confusion, or neck stiffness.
  • Sepsis (infection of the blood) – symptoms include fever, irritability, discoloured skin, vomiting, drowsiness, or difficulty with breathing.
  • Joint infection/inflammation (septic arthritis) – symptoms include joint pain redness, warmth or swelling.
  • Pneumonia (lung infection or inflammation) – symptoms include cough, fever, or difficulty breathing.
  • Necrotising fasciitis (infection of the soft tissue) – symptoms include redness, swelling and severe pain in the region where there is soft tissue infection.
  • Streptococcal toxic shock syndrome (STSS) – symptoms include high fever, low blood pressure, body rash, diarrhoea and vomiting, difficulty breathing, and kidney or liver damage.

A person with iGAS infection can become very ill within 12 to 24 hours so it is important to be aware of these early signs and symptoms and seek medical attention immediately if you develop these symptoms.


iGAS is diagnosed by isolation of GAS from parts of the body where these bacteria are not normally found such as blood, muscles or lungs.

Incubation period

(time between becoming infected and developing symptoms)

Incubation can be as short as 1 to 3 days, but can be up to 30 days depending on the site of infection and clinical illness.

Infectious period

(the  time during which an infected person can infect others)

Infectious for as long as these bacteria are carried on the skin. A person does not have to have symptoms of infection to be able to spread the bacteria (these people are called ‘carriers’).

Cases are infectious until 24 hours after initiation/commencement of appropriate antibiotics.


iGAS requires urgent treatment to minimise the risk of serious injury and death. This includes urgent antibiotic therapy and supportive measures. Urgent surgery may be required.

Close contacts2 of a person with iGAS infection do not usually require any treatment if they remain well, and secondary cases are rare. However, if you or someone in the household develop any of the symptoms of iGAS infection in the 30 days following contact with someone with an iGAS infection, seek medical advice immediately and tell the doctor you have been in contact with someone recently diagnosed with iGAS infection.


  • Clean your hands regularly with soap and water for 20 seconds or use an alcohol-based hand rub/sanitiser if your hands appear clean.
  • Cover your nose and mouth with a tissue when coughing and sneezing or use your elbow, not your hands.
  • These bacteria can spread on bed linen, towels and clothes, so wash these items regularly after use with a laundry detergent.
  • Keep wounds (like cuts or scrapes) clean to prevent infections. Wounds should be watched for possible signs of infection which may include increasing redness, swelling and pain at the wound site. If these signs occur, especially in a person who also has a fever, consult a doctor immediately.

Useful links


1 — In South Australia the law requires doctors and laboratories to report some infections or diseases to SA Health. These infections or diseases are commonly referred to as 'notifiable conditions'.

2 — A contact is any person who has been close enough to an infected person to be at risk of having acquired the infection from that person.