Invasive Group A streptococcal infection

Group A streptococci (GAS) are bacteria that occur frequently in healthy people. They usually do not cause diseases or these diseases are only mild in nature. However, in rare cases, they can cause severe “invasive” infections. 

What are invasive Group A streptococcal infections?

Group A Streptococcus (GAS), or Streptococcus pyogenes, occur frequently in the nose and throat, or on the skin, of healthy people. In young children in particular, these bacteria often also cause mild, superficial illnesses such as a sore throat (‘strep throat’), scarlet fever (‘scarlatina’) or impetigo. 

GAS can sometimes also penetrate parts of the body where bacteria don’t usually occur, such as deep in the muscles or in the cerebral spinal fluid. These are then known as ‘invasive infections’. Examples of invasive infections caused by GAS (iGAS) are sepsis, childbed fever (postpartum infections, puerperal fever) or meningitis. The most severe forms of iGAS are toxic shock (streptococcal toxic shock syndrome, STSS) or necrotising fasciitis (NF). When cases of NF are encountered, laypeople often talk about ‘flesh-eating bacteria’.  

Risk factors

A combination of factors, such as the host/patient, bacteria and the mode of transmission, determines whether or not someone will become (severely) ill when infected with GAS
Some bacterial strains are more dangerous than others because they produce more toxins, for example. Intense exposure to a patient with iGAS, such as for example an infected member of the household, also increases someone’s risk of developing iGAS. Wounds (such as following an operation or with a chickenpox infection) are a potential portal of entry for the bacteria. After giving birth, women are also particularly susceptible to an iGAS infection. Finally, we see iGAS infections more frequently in people with a weakened immune system, very young children or people aged over 65 years. 


GAS are usually transmitted via infected saliva droplets. When someone coughs, sneezes and talks, small droplets containing the bacteria are released into the air, which can then be inhaled by other people. Direct contact with pus or wound secretions also leads to infection. Infected droplets can also land on toys or cutlery, thus infecting others.


A lot of healthy people, especially children, are carriers of GAS. It is therefore difficult to prevent infections and there is no vaccine against severe illness. However, it is generally important to ensure good hygiene (regular hand washing, using a tissue when you sneeze, etc.) and certainly to correctly treat and clean wounds. In some cases, in consultation with the regional infection prevention service, preventative antibiotics may be given to other members of a household in which someone has iGAS. 


iGAS are severe infections which usually require admission to hospital. Treatment with antibiotics will always be started, although this could also include additional treatments or an operation to remove the infected tissue. 

Notifiable Disease

It is important (and obligatory) to notify the local infection prevention services of cases of iGAS, so that appropriate measures can be taken. The exact case definitions and notification modalities are different in the Brussels-Capital Region, Flanders and Wallonia

Sciensano monitors the epidemiology of iGAS infections in Belgium and contributes data to international scientific studies.

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