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Group A Streptococcal Infection

Group A streptococcal infections are caused by Streptococcus pyogenes, a species of beta-hemolytic Gramme-positive bacteria. These infections range from mild to severe and life-threatening, particularly if the bacteria enter the bloodstream, leading to invasive GAS (iGAS). Transmission occurs through direct contact with mucus or sores on the skin. Despite antibiotic treatments, cases of iGAS are rising, especially in Africa.

Streptococcus pyogenes
Streptococcus pyogenes

Types of Infection

GAS can cause both non-invasive and invasive infections:

  • Non-invasive infections are more common and less severe. These include:
    • Strep throat (pharyngitis): Affects 15–30% of childhood cases and 10% of adult cases.
    • Impetigo: A skin infection.
    • Scarlet fever: Less common, non-invasive infection.
  • Invasive infections are rarer but more severe. These occur when bacteria infect the blood or organs, leading to:
    • Streptococcal toxic shock syndrome (STSS)
    • Necrotising fasciitis (NF)
    • Pneumonia
    • Bacteraemia

Humans can be asymptomatic carriers of GAS on the skin or in the throat, being less contagious than symptomatic carriers.

Severe Infections

Certain GAS strains can cause severe infections, particularly in individuals with compromised immune systems, burn victims, elderly persons, those with diabetes or vascular disease, and intravenous drug users. Severe infections can lead to shock, multisystem organ failure, and death. Diagnostic tests include blood counts, urinalysis, and cultures of blood or wound fluid.

Example of a workup algorithm for possible bacterial infection
Example of a workup algorithm for possible bacterial infection


Diagnosis involves a swab of the affected area, followed by laboratory testing. A Gramme stain shows Gramme-positive cocci in chains, and the organism is cultured on blood agar. The rapid pyrrolidonyl arylamidase (PYR) test is commonly used, with a positive reaction indicating group A beta-hemolytic streptococci. Latex agglutination kits can also distinguish the main groups seen in clinical practice.


Effective hand hygiene is very important for preventing S. pyogenes infections. Currently, no vaccines are available, although research is ongoing. Challenges include the wide variety of S. pyogenes strains and the extensive trials needed for vaccine development.


The preferred treatment for GAS infections is penicillin for around 10 days. For penicillin-allergic individuals, erythromycin, other macrolides, and cephalosporins are effective. Deep oropharyngeal abscesses may require ampicillin/sulbactam, amoxicillin/clavulanic acid, or clindamycin, alongside aspiration or drainage. Streptococcal toxic shock syndrome and necrotising fasciitis require high-dose penicillin and clindamycin, with surgery often needed for necrotising fasciitis.

No penicillin resistance has been reported, but treatment failure usually results from patient noncompliance. In such cases, another course of antibiotics with cephalosporins is common. Several vaccines, including the 30-valent N-terminal M-protein-based vaccine and minimal epitope J8 vaccine, are approaching clinical studies.


GAS infections can lead to complications such as:

  • Post-streptococcal glomerulonephritis (PSGN): Involves kidney inflammation, presenting with dark-coloured urine, swelling, and high blood pressure.
  • Paediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS): Hypothesised to cause OCD and tic disorders in children.
  • Rheumatic fever: An inflammatory disease affecting the heart, joints, and other tissues.
  • Scarlet fever
  • Toxic shock syndrome

Acute Rheumatic Fever

Acute rheumatic fever (ARF) is a complication of respiratory infections caused by GAS. It is most common in children aged 5-15 and occurs 1-3 weeks after untreated GAS pharyngitis. Diagnosis is based on Jones Criteria, which include pancarditis, migratory polyarthritis, subcutaneous nodules, erythema marginatum, and Sydenham chorea. ARF can lead to chronic rheumatic heart disease, particularly affecting the mitral valve.

Post-Streptococcal Glomerulonephritis

PSGN is an uncommon complication of strep throat or streptococcal skin infection, classified as a type III hypersensitivity reaction. Symptoms develop within 10 days of a strep throat or 3 weeks of a GAS skin infection, leading to kidney inflammation. Clinical findings include pale skin, lethargy, loss of appetite, headache, and dull back pain. Treatment involves supportive care.


PANDAS is a controversial hypothesis suggesting that OCD and tic disorders in children are triggered by GABHS infections. While PANDAS remains unconfirmed, alternative hypotheses like PANS and CANS have been proposed, which include different mechanisms for acute-onset neuropsychiatric conditions but do not exclude GABHS infections as a cause in some cases.

Self-assessment MCQs (single best answer)

Which of the following bacteria is responsible for Group A streptococcal infections?

Which of the following is a non-invasive infection caused by Group A Streptococcus?

Which diagnostic test is commonly used to identify Group A beta-hemolytic streptococci?

Which treatment is preferred for Group A Streptococcus infections in penicillin-allergic individuals?

Which of the following is NOT a complication of Group A Streptococcal infections?

What is the primary method of transmission for Group A Streptococcal infections?

What type of hypersensitivity reaction is Post-Streptococcal Glomerulonephritis (PSGN)?

Which severe infection is characterised by rapid tissue destruction and often requires surgical intervention?

Which of the following groups is at a higher risk for severe Group A Streptococcal infections?

Which diagnostic method involves the culturing of the organism on blood agar to identify Group A Streptococcus?


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