Clinical Considerations for Group A Streptococcus

Key points

  • Streptococcus pyogenes are also called group A Streptococcus (group A strep bacteria).
  • Group A strep bacteria can cause both noninvasive and invasive disease.
  • They can also cause long-term sequelae.
  • The bacteria are contagious and usually spread via respiratory droplets.
Medical illustration of erythromycin-resistant group A Streptococcus.

Guiding principles


S. pyogenes are gram-positive cocci that grow in chains. They exhibit β-hemolysis (complete hemolysis) when grown on blood agar plates. They belong to group A in the Lancefield classification system for β-hemolytic Streptococcus, and thus are called group A streptococci.

This illustration depicts a photomicrographic view of Streptococcus pyogenes bacteria.
Streptococcus pyogenes on Gram stain.


Cause infections and immune-mediated sequelae

Learn about clinical features, complications, diagnosis, and treatment options for the following conditions related to group A strep bacteria.

Noninvasive diseases

Invasive diseases

Immune-mediated sequelae


Transmission is most often direct person-to-person spread through respiratory droplets. It can also occur through contact with secretions (e.g., saliva, wound discharge, nasal secretions) from an infected person.

Although rare, spread of group A strep bacteria may also occur via food.

Environmental transmission via surfaces and fomites may be possible. However, it's likely a less common route of transmission.

There's no evidence pets can transmit the bacteria to humans, the primary reservoir for group A strep bacteria.


Prevention activities vary by condition, but generally focus on three important goals:

  1. Limit exposure and spread of bacteria
  2. Treat group A strep infections
  3. Use preventive antibiotics when appropriate

Surveillance and trends

CDC tracks invasive group A strep disease. Streptococcal toxic shock syndrome is the only nationally notifiable disease caused by group A strep bacteria.