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micrograph of treptococcus pyogenese bacteria bound to a human neutrophil

Streptococcus pyogenese bacteria (yellow) bound to a human neutrophil (blue).
Credit: NIAID

Group A Streptococcal Infections

Group A streptococcal (GAS) infections can range from a mild skin infection or a sore throat to severe, life-threatening conditions. Most people are familiar with strep throat, which along with minor skin infections, is the most common form of the disease. Health experts estimate that more than 10 million mild infections (throat and skin) occur every year.

Types of GAS Infections

They also include severe, life-threatening strep infections such as

  • Bacteremia (bacteria in the blood)
  • Toxic shock syndrome
  • Necrotizing fasciitis (commonly called flesh-eating disease)


Untreated GAS infections can result in rheumatic fever and post-streptococcal glomerulonephritis (PSGN).

Rheumatic fever can develop about 18 days after a bout of strep throat and causes heart disease with or without joint pain. It can be followed months later by Sydenham chorea, a disorder in which the muscles of the torso, arms, and legs move involuntarily in a dancing and jerky manner.

PSGN is an inflammation of the kidneys that may follow an untreated strep throat but more often comes after a strep skin infection.

Both disorders are rarely seen in the United States because of prompt and effective treatment of most cases of strep throat.


Through research, health experts have learned that there are more than 120 different strains of group A streptococci bacteria, each producing its own unique proteins. Some of these proteins are responsible for specific GAS diseases.

With the support of NIAID, scientists have determined the genetic sequence, or DNA code, for five strains of the group A streptococcus bacterium.

By studying its genes, scientists can learn which proteins are responsible for virulence—crucial information that will lead to new and improved drugs and vaccines.

NIAID supports research to develop a group A streptococcus vaccine, and several candidate vaccines are in various phases of development. While some scientists are conducting animal model studies to obtain data to pursue clinical trials in humans, other scientists are close to evaluating group A streptococcus vaccine candidates in Phase I clinical trials.

As a result of NIAID-supported research, the first group A streptococcus vaccine clinical trial in 30 years was started. The vaccine was well tolerated by patients and has led to further clinical evaluation of a similar vaccine candidate.

An effective vaccine will prevent not only strep throat and impetigo but also more serious invasive disease and post-infectious complications like rheumatic fever.

Vaccine development efforts include NIAID-supported epidemiological studies:

  • To determine the extent of group A streptococcal disease
  • To characterize group A streptococcal strains causing illness in the United States and developing countries

NIAID, in collaboration with the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO), has developed standard definitions and methods for surveillance of group A streptococcal diseases to determine current burden of disease information.

This was accomplished by meetings with experts in the group A streptococcal research community that included research scientists, academic investigators, clinicians, and public health officials.


GAS diseases are a significant public health problem in both developing and developed countries. No vaccines are available for protection against GAS infections. Meetings supported by the National Institutes of Health and WHO have resulted in development of field protocols for standardized surveillance of GAS disease to obtain burden of disease data to 1) compare data across geographic sites; 2) develop sample size estimates and endpoints for vaccine clinical trials; and 3) increase awareness and attract investment for vaccine development and introduction.

Two field protocols were developed for NIAID clinical studies to compare epidemiological data across different geographical locations.

The field protocols were developed by working groups that included scientists and clinicians with expertise in GAS research and epidemiology from the United States and developing countries, representatives from WHO, and U.S. federal agencies (NIAID and CDC). These protocols have been implemented at NIAID-supported clinical sites in Mali (Africa), Leon (Nicaragua), Suva (Fiji), and Capetown (South Africa) to obtain epidemiological data that will be useful for designing future vaccine clinical trials. When all data from these clinical studies have been collected and analyzed, the protocols will be reviewed and updated as appropriate.

One protocol focused on acute streptococcal disease: Standardization of Epidemiologic Protocols for Surveillance of Acute Diseases Caused by Streptococcus pyogenes: Pharyngitis, Impetigo, and Invasive Diseases (PDF). The following publications describe data generated using this document:

The other protocol focused on the after-effects of acute infections: Standardization of epidemiologic protocols for surveillance of post-streptococcal sequelae: acute rheumatic fever, rheumatic heart disease and acute post-streptococcal glomerulonephritis (PDF). The following publications describe data generated using this document:

These protocols are posted to make them more widely available to the scientific community and were used at NIAID-supported clinical sites in Mali (Africa), Leon (Nicaragua), and Suva (Fiji) to obtain epidemiological data that will be useful for designing future vaccine clinical trials. When all data from these clinical studies have been collected and analyzed, the protocols will be reviewed and updated as appropriate.

NIAID Workshop: Prevention of Group A Strep Diseases and their Sequelae

A workshop to discuss the prevention of GAS diseases and their sequelae with a focus on vaccine-related issues was held in Bethesda, Maryland, in 2004 with support from the National Vaccine Program Office and NIAID.


Last Updated September 29, 2015