Bacteria, Epidemiology, Infectious Diseases, Microbiology, rare infectious disease

Severe Strep iGAS: Invasive Group A Streptococcus Infections Rising?

Author Chandana Balasubramanian , 25-Jan-2024

In most cases, strep throat is not very serious. However, there is a more dangerous form of the infection called invasive Group A streptococcus (iGAS). iGAS can lead to serious illnesses like sepsis, meningitis, and pneumonia. 


Unfortunately, in 2024, there has been a notable increase in Group A streptococcal infections, mainly in children under 10, including deaths in Canada and Europe. 


This situation has been a cause of concern among public health experts because Group A streptococcus bacteria are crafty. They are great at finding new ways to avoid a host’s immune system and defenses.


The good news is that severe cases are still rare. Still, it’s best to stay aware of how Group A strep is spread, the epidemiology, symptoms, diagnosis, treatment, and how to minimize your risk of getting an invasive Group A strep infection.


What is invasive Group A streptococcus (iGAS)?

Invasive GAS disease is a severe and sometimes life-threatening infection where a type of streptococcus bacteria invade parts of the body like the blood, deep muscles, fat tissues, or the lungs. 

iGAS is caused by streptococcus pyogenes, also known as Group A Streptococcus, a type of bacteria that, according to WHO, causes 500,000 deaths each year.


  • The word ‘streptococcus’ literally means chain (Strepto) and berry (coccus).
  • 1874: The first description of streptococcal infection was given by Austrian surgeon Theodor Billroth. He described the bacteria as small organisms isolated or in pairs, sometimes linked as chains. 
  • 1879: Louis Pasteur isolated streptococcus from women with puerperal fever. This experiment proved that the pathogen was responsible for the highest mortality rates during that time.
  • 1903: Hugo Schottmuller invented agar plates, an innovation that helped researchers identify different types of streptococcus bacteria.
  • 1928: The landmark discovery of penicillin by Alexander Fleming paved the way for treating Group A streptococcal infections.
  • 1933: Rebecca Lancefield used variations in surface antigens to divide streptococci into groups from A-X. Strains from diseases affecting humans were categorized as Group A.



Streptococcus pyogenes is more likely to circulate during winter and early spring. These GAS bacteria are the most common cause of bacterial pharyngitis in children.

Usually, the pathogen causes relatively milder illnesses like strep throat or scarlet fever. However, the severe form, iGAS, can be fatal. 

The Group A streptococcus or GAS infections are responsible for more than 500,000 deaths a year globally. As a result, in 2018, WHO prioritized the need for effective prevention against GAS by publishing a roadmap for GAS vaccine development.

Who is most at risk for iGAS?

Children who have viral infections like chickenpox (varicella) or the flu are more likely to get iGAS disease, according to the World Health Organization (WHO). 

Other groups at higher risk for iGAS disease include:

  • Children under 5 years old, especially babies
  • Women who are pregnant or have recently given birth
  • Older individuals aged 65 and above
  • People who do not have easy access to clean and hygienic facilities
  • Those who live in crowded places or spend a lot of time in such conditions
  • Individuals with weak immune systems or ongoing health problems.


How is it spread?

Streptococcus bacteria survive in the throat and on the skin for a while, making it easy for them to spread when people sneeze or have direct contact with infected skin.

People with a GAS infection who do not have any symptoms are considered ‘colonized.’ Colonized individuals and those sick with a GAS infection can spread the disease to others.


Biology of the disease

Group A streptococci can enter the human body through various routes, primarily through respiratory droplets, when an infected person coughs or sneezes. They can also enter through breaks in the skin, like cuts or surgical wounds.

Once inside, these bacteria quickly adapt to the body’s environment and start reproducing. They adhere to the mucous membranes in the throat and respiratory tract or invade deeper tissues and organs.

  • In cases like strep throat (pharyngitis), the bacteria primarily replicate in the throat and tonsils. 
  • In skin infections like impetigo or cellulitis, they multiply in the layers of the skin.
  • In invasive group A streptococcus infections (iGAS), the bacteria can enter the bloodstream and deep muscle and fat tissues or even reach the lungs. This can lead to severe conditions like sepsis, necrotizing fasciitis, or pneumonia.


How do Group A streptococcus bacteria cause infection? 

Group A streptococci produce various toxins and enzymes that damage host tissues

For example, they can break down the proteins in tissues, leading to tissue destruction and the characteristic symptoms of infection. These toxins can enter the bloodstream in severe cases, causing systemic inflammation and organ damage. The host’s immune response also plays a role in the severity of the infection.

So, these bacteria enter the host and multiply. Their destructive actions and the body’s immune response lead to infections ranging from mild, like strep throat, to severe and life-threatening, like invasive group A streptococcus infections.



Early symptoms include:

  • high fever
  • severe muscle aches
  • localized tenderness in muscles
  • increasing pain, swelling, and redness at the site of the wound
  • unexplained diarrhea or vomiting.


In rare cases, Group A strep infections become invasive or iGAS. Here, the bacteria enters the blood or deep in the tissues to cause severe, life-threatening infections like sepsis (blood infection), meningitis (brain inflammation), or pneumonia. 

iGAS can show up as:

  • Pharyngitis or a throat infection
  • Tonsillitis or a tonsil infection
  • Skin infection or cellulitis
  • Skin sores or impetigo
  • Necrotizing fasciitis (flesh-eating bacteria).



Invasive Group A Streptococcus (iGAS) infections can be diagnosed through clinical evaluation and laboratory tests. 

These include: 

  • Physical evaluation: A healthcare provider will examine the patient and take a detailed medical history. They will look for symptoms and signs of severe infection, which may include fever, severe pain, redness, and tissue swelling.
  • Blood tests: Testing a blood sample for streptococcus pyogenes (Group A Streptococcus) bacteria in the bloodstream is necessary  to confirm the diagnosis of an invasive infection.
  • Tissue biopsy: A tissue biopsy may be performed in cases like necrotizing fasciitis or deep-seated abscesses. This involves removing a small sample of infected tissue for laboratory analysis to identify the bacteria and assess the extent of tissue damage.
  • Throat swab or nasal swab: This is more relevant for diagnosing strep throat. Although less common for diagnosing invasive infections, swabs of the throat or nasal passages may be taken to identify the presence of Group A Streptococcus.
  • Imaging scans: X-rays, CT scans, or MRI scans may be ordered to visualize the affected areas. These imaging studies help assess the extent of tissue involvement, especially in cases where deeper tissues or organs are affected.


The exact tests and sequence of testing depend on the type of infection, location, and severity of disease, and early medical attention is required to manage iGAS infections. 



Invasive Group A staph infections can be treated with antibiotics, but they need immediate medical care, commonly penicillin. Clindamycin may be used if the infected person is allergic to penicillin.

In rare cases, depending on the severity of the infection, some type of surgical intervention or procedure may be required. For example, abscesses may need to be drained, localized infected tissue may be removed, or, in extremely severe cases, amputation.



Unfortunately, there is no vaccine to protect against iGAS or GAS infections. This situation concerns healthcare professionals because streptococcus Group A bacteria are demonstrating signs of antibiotic resistance. 

However, other preventive measures can help minimize the spread.

Good hygiene practices

Wash your hands with soap and water for at least twenty seconds. This is particularly necessary after coughing, sneezing, using the bathroom, or touching potentially contaminated surfaces.

Use hand sanitizers with at least 60% alcohol when soap and water are not readily available. Avoid touching your face, especially eyes, nose, and mouth, with unwashed hands.

Respiratory hygiene

Cover your mouth and nose when you cough or sneeze; avoid using your hands. Use a tissue or your elbow to minimize the risk of spread. 

Dispose of used tissues in a closed container and wash your hands immediately. Minimize interactions with individuals who have respiratory infections, such as the flu or a cold.

Wound care

Properly clean and care for any cuts, scrapes, or wounds to prevent bacterial entry. Keep wounds covered with a clean bandage until they heal.

Practice preventive health measures to build immunity

Eat a balanced diet and get regular exercise and adequate sleep to support a robust immune system. Manage chronic conditions under medical supervision.

Avoid sharing personal items

Do not share items like towels, razors, or eating utensils with others.

Vaccination against other respiratory infections

Consider getting vaccinated against vaccine-preventable diseases, such as influenza (flu) and pneumococcal infections, which can reduce the risk of secondary infections.

Receive prompt medical attention

If you develop symptoms like fever, severe pain, skin changes, or any signs of infection, seek immediate medical attention. Early diagnosis and treatment are important to manage iGAS infections effectively.

These measures can help reduce the risk of iGAS infections and their complications. However, complete prevention cannot be guaranteed due to the presence of Group A Streptococcus bacteria in the environment.



The increase in invasive Group A Streptococcus (iGAS) infections, especially among children under 10, is concerning. These bacteria are known for evading the body’s immune system and pose a significant public health challenge, with signs of antibiotic resistance emerging.

While severe cases are still relatively rare, staying informed about iGAS infections, including their spread, symptoms, diagnosis, and treatment, is crucial.

Preventive measures like good hygiene, maintaining overall health, avoiding sharing personal items, considering vaccinations against respiratory infections, and seeking prompt medical attention for symptoms can reduce the risk of iGAS infections. 

While there’s no specific iGAS vaccine yet, these actions may protect public health and prevent the spread of this potentially life-threatening infection.


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Learn more about streptococcus infections and other infectious diseases on the GIDEON platform.


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Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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