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Streptococcal Infections

(Strep Infections)


Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Reviewed/Revised Mar 2023
Topic Resources

Streptococcal infections are caused by any one of several species of Streptococcus. These gram-positive Overview of Gram-Positive Bacteria Gram-positive bacteria are classified by the color they turn after a chemical called Gram stain is applied to them. Gram-positive bacteria stain blue when this stain is applied to them. (Other... read more , sphere-shaped (coccal) bacteria (see figure ) cause many disorders, including strep throat, pneumonia, and wound, skin, heart valve, and bloodstream infections.

  • Different groups of these bacteria are spread in different ways—for example, through coughing or sneezing, through contact with infected wounds or sores, or during vaginal delivery (from mother to child).

  • These infections affect various areas of the body, including the throat, middle ear, sinuses, lungs, skin, tissue under the skin, heart valves, and bloodstream.

  • Symptoms may include red and painful swollen tissues, scabby sores, sore (strep) throat, and a rash, depending on the area affected.

  • Doctors may be able to diagnose the infection based on symptoms and can confirm the diagnosis by identifying the bacteria in a sample of infected tissue, sometimes supplemented with imaging tests.

  • Antibiotics are given by mouth or, for serious infections, by vein.

Many species of streptococci live harmlessly in and on the body. Some species that can cause infection are also present in some healthy people but cause no symptoms. These people are called carriers.

Types of streptococci

Streptococci are divided into groups based on their appearance when grown in the laboratory and on their different chemical components. Each group tends to produce specific infections. Groups that are most likely to cause diseases in people include


Spread of streptococcal infection

Group A streptococci are spread through the following:

  • Inhalation of droplets of secretions from the nose or throat that are dispersed when an infected person coughs or sneezes

  • Contact with infected wounds or sores on the skin

Usually, the bacteria are not spread through casual contact, but they may spread in crowded environments such as dormitories, schools, and military barracks. After 24 hours of antibiotic treatment, people no longer can spread the bacteria to others.

Group B streptococci can be spread to newborns through vaginal secretions during vaginal delivery.

Viridans streptococci inhabit the mouth of healthy people but can invade the bloodstream, especially in people with periodontal inflammation, and infect heart valves (causing endocarditis Infective Endocarditis Infective endocarditis is an infection of the lining of the heart (endocardium) and usually also of the heart valves. Infective endocarditis occurs when bacteria enter the bloodstream and travel... read more Infective Endocarditis ).

Symptoms of Strep Infections

Symptoms of streptococcal infections vary, depending on where the infection is:

Scarlet fever is uncommon today, but outbreaks still occur. It tends to spread when people have close contact with each other—for example, in schools or day care centers. Scarlet fever occurs mainly in children, usually after strep throat but sometimes after streptococcal skin infections.

Complications of streptococcal infections

Toxic shock syndrome Toxic Shock Syndrome Toxic shock syndrome is a group of rapidly progressive and severe symptoms that include fever, rash, dangerously low blood pressure, and failure of several organs. It is caused by toxins produced... read more causes rapidly progressive and severe symptoms that include fever, rash, dangerously low blood pressure, and failure of several organs. It is caused by toxins produced by group A streptococci or Staphylococcus aureus.

Diagnosis of Strep Infections

  • For strep throat, rapid tests and/or culture of a sample taken from the throat

  • For cellulitis and impetigo, often a doctor's evaluation

  • For necrotizing fasciitis, an imaging test (such as CT), culture, and often exploratory surgery

Different streptococcal diseases are diagnosed differently.

Strep throat

Doctors suspect strep throat based on the following:

  • Fever

  • Enlarged and tender lymph nodes in the neck

  • Pus in or on the tonsils

  • Absence of cough

The main reason for diagnosing strep throat is to reduce the chance of developing complications (such as rheumatic fever Rheumatic Fever Rheumatic fever is inflammation of the joints, heart, skin, and nervous system, resulting from a complication of untreated streptococcal infection of the throat. Rheumatic fever is a reaction... read more Rheumatic Fever ) by using antibiotics. Because symptoms of group A strep throat are often similar to those of throat infection due to a virus (and viral infections should not be treated with antibiotics), testing with a throat culture or another test is necessary to confirm the diagnosis and to determine how to treat the infection.

Several diagnostic tests (called rapid tests) can be completed in minutes. For these tests, a swab is used to take a sample from the throat. If these results indicate infection (positive results), the diagnosis of strep throat is confirmed, and a throat culture, which takes longer to process, is not needed. However, results of rapid tests sometimes indicate no infection when infection is present (called false-negative results). If results are negative in children and adolescents, culture is needed. A sample taken from the throat with a swab is sent to a laboratory so that group A streptococci, if present, can be grown (cultured) overnight. In adults, negative results do not require confirmation by culture because the incidence of streptococcal infection and risk of rheumatic fever in adults is so low.

Close contacts of a person with a streptococcal infection should be checked for the bacteria if they have symptoms or have ever had complications due to streptococcal infection.

Did You Know...

  • Doctors cannot tell just by looking whether a sore throat is caused by a streptococcal infection or a virus. A strep culture test is needed.

Cellulitis and impetigo

Cellulitis and impetigo can often be diagnosed based on symptoms, although culture of a sample taken from impetigo sores can often help doctors identify other microorganisms that may be the cause, such as Staphylococcus aureus.

Necrotizing fasciitis

To diagnose necrotizing fasciitis, doctors frequently use x-rays, computed tomography (CT), or magnetic resonance imaging (MRI) and culture. Exploratory surgery is often required to confirm the diagnosis.

Treatment of Strep Infections

  • Antibiotics (usually penicillin)

  • For necrotizing fasciitis, surgery to remove dead tissue

Strep throat

Strep throat usually resolves within 1 to 2 weeks, even without treatment.

Antibiotics shorten the duration of symptoms in young children but have only a modest effect on symptoms in adolescents and adults. Nevertheless, antibiotics are given to help prevent the spread of the infection to the middle ear, sinuses, and mastoid bone, as well as to prevent spread to other people. Antibiotic therapy also helps prevent rheumatic fever, although it may not prevent kidney inflammation (glomerulonephritis). Usually, antibiotics do not need to be started immediately. Waiting 1 to 2 days for culture results before starting antibiotics does not increase the risk of rheumatic fever. An exception is when a family member has or has had rheumatic fever. Then, every streptococcal infection in any family member should be treated as soon as possible.

Usually, penicillin or amoxicillin is given by mouth for 10 days. One injection of a long-lasting penicillin (benzathine) can be given instead. People who cannot take penicillin can be given erythromycin, clarithromycin, or clindamycin by mouth for 10 days or azithromycin for 5 days.

The bacteria that cause strep throat have never been resistant to penicillin. In the United States, about 5 to 10% of these bacteria are resistant to erythromycin and related antibiotics (azithromycin and clarithromycin), but in some countries, more than 10% are resistant.

Fever, headache, and sore throat can be treated with acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs), which reduce pain and fever. However, children should not be given aspirin because it increases the risk of Reye syndrome Reye Syndrome Reye syndrome is a very rare but life-threatening disorder that causes inflammation and swelling of the brain and impairment and loss of function of the liver. The cause of Reye syndrome is... read more .

Neither bed rest nor isolation is necessary.

Other streptococcal infections

Prompt treatment with antibiotics can prevent streptococcal infection from spreading rapidly and reaching the blood and internal organs. Consequently, cellulitis is often treated without doing a culture to identify the bacteria that are causing it. In such cases, doctors use antibiotics that are effective against both streptococci and staphylococci (such as dicloxacillin or cephalexin).

Serious streptococcal infections (such as necrotizing fasciitis, endocarditis, and severe cellulitis) require penicillin, given intravenously, sometimes with other antibiotics.

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

Centers for Disease Control and Prevention (CDC): Group A Streptococcal (GAS) Disease: Information about diseases caused by group A strep

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