Invasive Group A Streptococcal Disease

Group A Streptococcus (GAS) is a bacterium often found in the throat and on the skin. The most common infections caused by GAS are sore throat (“strep throat”) and skin infections such as impetigo and cellulitis. Other diseases may occur following GAS infections such as acute rheumatic fever (a disease affecting the heart and joints) and post-streptococcal glomerulonephritis (a disease affecting the kidneys).

Severe, sometimes life-threatening GAS disease may occur when the bacteria get into parts of the body where bacteria are not normally found, such as the blood, muscle or lungs. These infections are called invasive GAS (iGAS) disease. People at higher risk of iGAS infection are the very young, the very old and people with weak immune systems.

Signs and Symptoms: 

A person with iGAS infection can become very ill within 12 – 24 hours. Early signs and symptoms of iGAS may include:

  • High fever
  • Severe muscle aches
  • Localised muscle tenderness
  • Sometimes redness at the site of a wound

Symptoms of iGAS can depend on where the infection is in the body. Most people who come into contact with GAS remain well and symptom-free, or develop throat and skin infections. If you develop any of these symptoms after having contact with a person diagnosed with iGAS, please seek medical advice immediately. Tell your doctor that you have been in contact with someone recently diagnosed with iGAS disease and that you have developed some symptoms that you are worried about.


Prompt antibiotic therapy is required for iGAS disease and most people need admission to hospital for supportive treatment. People with necrotising fasciitis may require surgery to remove damaged tissue.


Streptococci survive in throats and on hands for long enough to allow easy spread between people through coughing, sneezing, kissing or skin contact. People may sometimes carry the bacteria in their throat or skin without any symptoms of illness. They are known to be ‘colonised’ with the bacteria.

Invasive GAS (iGAS) infections can occur when the bacteria get past a person’s defences. This may happen when a person has sores or breaks in the skin that allow the bacteria to get into the tissue, or when the person’s ability to fight infection is decreased because of chronic illness or an illness that affects the immune system.

Healthy people can sometimes get iGAS infection from close contacts such as a family member but this is rare.


To reduce the spread of bacteria it is important to wash hands, especially after coughing and sneezing and before preparing, eating or serving foods. People with “strep throats” should stay at home for at least 24 hours after starting a course of an effective antibiotic. In special situations (e.g. if spread of iGAS has been identified) people who are identified as carrying the bacteria may be required to stay at home for longer.

Health outcome: 

The course of disease depends on where the infection is in the body, the person’s immune system, and access to prompt and appropriate treatment.

Twoof the most severe forms of iGAS are necrotising fasciitis (a severe infection involving areas of soft tissue below the skin) and streptococcal toxic shock syndrome (a rapidly worsening illness where blood pressure is very low and organs within the body may fail). These severe iGAS infections have a higher chance of complications. Some people with iGAS infection may not survive. People who survive iGAS infection can sometimes develop long term disability.

Other resources: 

13Health (call 13 43 25 84)


Heymann, D., Ed. 2015. Control of Communicable Diseases Manual, 20th edition. Washington, DC: American Public Health Association

Public Health England 2013. Invasive Group A Streptococcal Infections: Factsheet for close contacts of cases.

Northern Territory Government 2016. Group A Streptococcal Disease (PDF 302kB)

Carr JP, Curtis N, Smeesters PR, Steer A 2016. Question 1: Are household contacts of patients with invasive group A streptococcal disease at higher risk of secondary infection? Archives of Diseases in Childhood 101: 198–201