Group A Streptococcus (GAS) is a bacterium commonly found in the throat and on the skin. The letter A refers to a classification of bacteria in the genus Streptococcus according to the composition of the cell wall of the organism. Group A streptococci can be present in the throat or on the skin and cause no symptoms of disease, but they may also cause infections that range from mild to severe and even life-threatening.
The majority of GAS infections are relatively mild illnesses, such as "strep throat" or impetigo. Occasionally, however, these bacteria can reach parts of the body where bacteria are not usually found, such as the blood, deep muscle and fat tissue, or the lungs, and can cause invasive infections. Two of the most severe but least common forms of invasive GAS disease are necrotizing fasciitis and streptococcal toxic shock syndrome. Necrotizing fasciitis (sometimes described by the media as "the flesh-eating bacteria") is a destructive infection of muscle and fat tissue; streptococcal toxic shock syndrome is a rapidly progressing infection causing shock and injury to internal organs such as the kidneys, liver, and lungs.
How are group A streptococci spread?
Group A streptococci are spread by direct contact with secretions from the nose and throat of infected persons or by contact with infected wounds or sores on the skin. The risk of spreading the infection is highest when a person is ill, such as with "strep throat" or an infected wound. Persons who carry the bacteria but have no symptoms are much less contagious. Treatment of infected persons with an appropriate antibiotic for 24 hours or longer generally eliminates their ability to spread the bacteria. Household items like plates, cups, or toys probably do not play a major role in disease transmission.
Why does invasive group A streptococcal disease occur?
Invasive group A streptococcal infections occur when the bacteria get past the defenses of the person who is infected. This may occur when a person has sores or other breaks in the skin that allow the bacteria to get into the tissue. Health conditions that decrease a person's immunity to infection also make invasive disease more likely. In addition, certain strains of group A streptococci are more likely to cause severe disease than others.
How common is invasive group A streptococcal disease?
Approximately 10,000 to 15,000 cases of invasive GAS disease occur in the United States each year, resulting in over 2,000 deaths. CDC estimates that 500 to 1,500 cases of necrotizing fasciitis and 2,000 to 3,000 cases of streptococcal toxic shock syndrome occur each year in the United States. Approximately 20% of patients with necrotizing fasciitis die, and 60% of patients with streptococcal toxic shock syndrome die. About 10% to 15% of patients with other forms of invasive group A streptococcal disease die. In contrast, several million persons get "strep throat" and impetigo annually.
Who is most at risk of getting invasive group A streptococcal disease?
Few people who come in contact with a virulent strain of GAS will develop invasive GAS disease; many will have a routine throat or skin infection, and most will have no symptoms whatsoever. Although healthy people can get invasive GAS disease, those with chronic illnesses like cancer, diabetes, and kidney disease requiring dialysis and those who use medications such as steroids are at higher risk. In addition, breaks in the skin, like cuts, wounds, or chickenpox may provide an opportunity for the bacteria to enter the body.
What are the early signs and symptoms of necrotizing fasciitis and streptococcal toxic shock syndrome?
Early signs and symptoms of necrotizing fasciitis include fever, severe pain and swelling, and redness at the wound site. Early signs and symptoms of streptococcal toxic shock syndrome may include fever, dizziness, confusion, diffuse red rash, and abdominal pain. Unfortunately, no sign or symptom is particular only to streptococcal toxic shock syndrome, making it sometimes difficult to differentiate from other illnesses.
How is group A streptococcal disease treated?
GAS infections can be treated with many different antibiotics. Early treatment may reduce the risk of death in cases of invasive disease, although even appropriate therapy does not prevent death in every case. It is always important to complete the entire course of antibiotics as prescribed.
What can be done to help prevent invasive group A streptococcal infections?
The spread of all types of GAS infections may be reduced by good handwashing, especially after coughing and sneezing, before preparing foods and before eating. Persons with sore throats should be seen by a doctor who can perform tests to find out whether it is "strep throat"; if so, the person should stay home from work, school, or day care until 24 hours or more after taking an antibiotic. All wounds should be kept clean and watched for possible signs of infection: increasing redness, swelling, drainage, and pain at the wound site. A person with signs of an infected wound, especially if fever develops, should seek medical care.
NCID Homepage Division of Bacterial and Mycotic Diseases HomepageUpdated: Wednesday, November 20, 1996