Group A Streptococcal Infections, NIAID Fact Sheet: NIAID


Article title: Group A Streptococcal Infections, NIAID Fact Sheet: NIAID
Conditions: Group A Streptococcal Infections, Strep, Strep throat, Scarlet fever, Impetigo, Cellulitis, group A streptococci, Bacteremia, Streptococcal toxic shock syndrome, Necrotizing fasciitis, Acute rheumatic fever, Post streptococcal glomerulonephritis
Source: NIAID
March 1999

Group A Streptococcal Infections

Organism: Streptococcus pyogenes

The group A streptococcus bacterium is responsible for most cases of streptococcal illness. Other types (B, C, D, and G) may also cause infection. Group B streptococci cause most streptococcal infections in newborns and maternal post-labor/delivery infections.

Some of the major syndromes associated with group A strep infection are:

  • streptococcal pharyngitis or "strep throat"
  • scarlet fever, most often preceded by a sore throat
  • skin infections (impetigo, cellulitis/erysipelas)
  • focal infections, limited to a particular body site, e.g., pneumonia, septic arthritis
  • bacteremia, sepsis, streptococcal toxic shock syndrome
  • necrotizing fasciitis
  • the complications of streptococcal infections, acute rheumatic fever and poststreptococcal glomerulonephritis


Signs and Symptoms: The signs and symptoms of strep throat are red, sore throat with white patches on tonsils, swollen lymph nodes in neck, fever, and headache. Nausea, vomiting, and abdominal pain more common in children.

Transmission: The illness is spread by direct, close contact with patients via respiratory droplets (coughing or sneezing). Casual contact rarely results in transmission. Rarely, contaminated food, especially milk and milk products, can result in outbreaks. Untreated patients are most infectious for 2-3 weeks after onset of infection. Incubation period, the period after exposure and before symptoms show up, is 2-4 days. Patient is no longer infectious within 24 hrs. after treatment begins.

Diagnosis: Throat is swabbed for culture or for a rapid strep test (10-20 minutes) which can be done in the doctor's office. If the rapid test is negative, a follow-up culture (which takes 24-48 hrs.) may be performed. A negative culture suggests a viral infection, in which case antibiotic treatment should be withheld or discontinued.

Treatment: Antibiotic treatment will reduce symptoms, minimize spread (transmission), and reduce the likelihood of complications. Treatment consists of penicillin (oral drug for 10 days; or single intramuscular injection of penicillin G). Erythromycin is recommended for penicillin-allergic patients. Second-line antibiotics include amoxicillin, clindamycin, and oral cephalosporins. Although symptoms subside within 4 days even without treatment, it is very important to complete the full course of antibiotics to prevent complications.


Scarlet fever is a streptococcal infection that occurs most often in association with a sore throat and rarely with impetigo or other streptococcal infections. It is characterized by sore throat, fever and a rash over the upper body that may spread to cover almost the entire body.

Signs and Symptoms: Persons with scarlet fever have a characteristic rash that is fine, red, rough-textured and blanches upon pressure. Scarlet fever also produces a bright red tongue with "strawberry" appearance. The skin often "desquamates," or peels, after recovery, usually on tips of fingers and toes.

Transmission: The illness is spread by the same means as strep throat.

Treatment: Other than the occurrence of the rash, the treatment and course of scarlet fever are no different from those of any strep throat.



Impetigo is a superficial skin infection most common among children age 2-6 years. Skin infections are usually caused by different streptococci strains than those that cause strep throat.

Signs and Symptoms: One or more pimple-like lesion surrounded by reddened skin. Lesions fill with pus, then break down over 4-6 days and form a thick crust. Impetigo is often associated with insect bites, cuts, and other forms of trauma to the skin. Itching is common. Scratching may spread the lesions.

Transmission: The infection is spread by direct contact with lesions or with nasal carriers. The incubation period is 1-3 days. Dried streptococci in the air are not infectious to intact skin.

Diagnosis: The diagnosis is made based on the typical appearance of the skin lesion.

Treatment: Topical or oral antibiotics are usually prescribed.


This illness results in inflammation of skin and underlying tissues.

Signs and Symptoms: The skin is painful, red, and tender. Patients experience fever and chills.  Lymph nodes may be swollen. The skin may blister and then scab over. Perianal cellulitis may also occur with itching and painful bowel movements. The erysipelas rash may occur on face, arms, or legs and has raised borders. The infection may recur, causing chronic swelling of extremities (lymphadenitis).

Transmission: Cellulitis begins with minor trauma, such as a bruise, usually to an extremity.

Diagnosis: The organism may be cultured from skin lesions or recovered from blood.

Treatment: Depending on the severity, treatment involves either oral or intravenous antibiotics.


Some strains of group A streptococci (GAS) cause severe infection. Those at greatest risk include children with chickenpox; persons with suppressed immune systems; burn victims; elderly persons with cellulitis, diabetes, blood vessel disease, or cancer; and persons taking steroid treatments or chemotherapy. Intravenous drug users also are at high risk. Severe GAS disease may also occur in healthy persons with no known risk factors. All severe GAS infections may lead to shock, multisystem organ failure, and death. Early recognition and treatment are critical. Diagnostic tests include blood counts and urinalysis as well as cultures of blood or fluid from a wound site. Antibiotics of choice include penicillin, erythromycin, and clindamycin.

Bacteremia: An invasion of bacteria into the bloodstream. Once in the bloodstream, the infection can spread to other parts of body, producing abscesses, peritonitis (inflammation of abdominal cavity), endocarditis (inflammation of the heart), or meningitis. Bacteremia may lead to sepsis or shock, causing a systemic illness with high fever, blood coagulation (thickening) and eventually organ failure.

Focal infections with or without bacteremia: GAS can cause focal infections, which are limited to a particular site.  These include pneumonia, abscess of tissues near the tonsils, joint infections (septic arthritis), bone infections (osteomyelitis), peritonitis, and meningitis. Bacteremia can be associated with these infections, but it is not always present. Treatment depends on the specific clinical findings.

Toxic shock syndrome: Streptococcal toxic shock syndrome begins with flu-like symptoms (fever, chills, and muscle aches). Pain is common, usually in an extremity, sometimes in the abdomen or chest. The condition progresses to confusion and coma. Blood pressure drops, kidneys malfunction, and soft tissues may be infected. The source of streptococcus, when identified, is most often the site of a minor wound or bruise. The syndrome occurs most often in healthy adults between the ages of 20-50.

Necrotizing fasciitis: A serious but rare infection (fascia) of the deeper layers of skin and fatty subcutaneous tissues. While many other types of bacteria can cause necrotizing fasciitis, most cases result from GAS.

The infection rarely starts with a sore throat. It more often begins at a site of minor, or sometimes no apparent, trauma. The affected skin is very painful, red, hot and swollen. Skin color may progress to violet and blisters may form, with subsequent necrosis (death) of subcutaneous tissues. Patients with necrotizing fasciitis typically have a fever and appear very ill. More severe cases progress within hours, and the death rate is high. Neocrotizing fasciitis is diagnosed by either blood cultures or aspiration of pus from tissue. Surgical exploration may be necessary. Early medical treatment is critical. Treatment often includes intravenous penicillin and clindamycin, along with aggressive surgical debridement (removal of infected tissue). Limb amputation may be necessary.

Complications of group A streptococcal infections:

Acute rheumatic fever (ARF) is a complication of a strep throat caused by particular strains of GAS. Although common in developing countries, ARF is rare in the United States, with small isolated outbreaks reported only occasionally. It is most common among children between 5-15 years of age. A family history of ARF may predispose an individual to the disease. Symptoms typically occur 18 days after an untreated strep throat. An acute attack lasts approximately 3 months. The most common clinical finding is a migratory arthritis involving multiple joints. The most serious complication is carditis, or heart inflammation (rheumatic heart disease), as this may lead to chronic heart disease and disability or death years after an attack. Less common findings include bumps or nodules under the skin (usually over the spine or other bony areas) and a red expanding rash on the trunk and extremities that recurs over weeks to months. Because of the different ways ARF presents itself, the disease may be difficult to diagnose. A neurological disorder, chorea, can occur months after an initial attack, causing jerky involuntary movements, muscle weakness, slurred speech, and personality changes. Initial episodes of ARF as well as recurrences can be prevented by treatment with appropriate antibiotics.

Post streptococcal glomerulonephritis (PSGN) is an uncommon complication of either a strep throat or a streptococcal skin infection. Symptoms of PSGN develop within 10 days following a strep throat or 3 weeks following a GAS skin infection. PSGN involves inflammation of the kidney. Symptoms include pale skin, lethargy, loss of appetite, headache and dull back pain. Clinical findings may include dark-colored urine, swelling of different parts of the body (edema), and high blood pressure. Treatment of PSGN consists of supportive care.


Through research, we have learned that there are more than 80 different variants of group A streptococci, each producing its own unique proteins. Some of these proteins are responsible for specific group A streptococcal syndromes. With the support of the National Institute of Allergy and Infectious Diseases, scientists have determined the genetic sequence, or DNA code, for more than 95 percent of the group A streptococcus organism. By studying an organismís genes we learn which proteins are responsible for virulence, crucial information that will lead to new and improved drugs and vaccines.

Funds from NIAID are supporting research for the development of a broadly-effective GAS vaccine. It is expected that this vaccine will prevent not only strep throat and impetigo, but more serious invasive disease and post-infectious complications like rheumatic fever.

Additional information on group A strep infection is available through MEDLINE Plus, a service of the National Library of Medicine. You can access MEDLINE Plus at the following Web site: If you do not have Internet access, ask a librarian for assistance.

NIAID, a component of the National Institutes of Health (NIH), supports research on AIDS, tuberculosis, malaria, and other infectious diseases, as well as allergies and immunology.  NIH is an agency of the U.S. Public Health Service, U.S. Department of Health and Human Services.

Press releases, fact sheets, and other NIAID-related materials are available on the NIAID Web site at

Prepared by:
Office of Communications and Public Liaison
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892

Public Health Service
U.S. Department of Health and Human Services

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