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Streptococcal Infections

(Strep Infections)


Larry M. Bush

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

Last full review/revision Mar 2021| Content last modified Mar 2021
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Streptococcal infections are caused by any one of several species of Streptococcus. These gram-positive, sphere-shaped (coccal) bacteria (see figure How Bacteria Shape Up) 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.

(See also Overview of Bacteria.)

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

One species—Streptococcus pneumoniae (pneumococci)—is usually considered separately (see Pneumococcal Infections).


Streptococci and Some Disorders They Cause




Group A

Streptococcus pyogenes

Ears, nose, and throat

Middle ear infection (otitis media)

Sore throat (pharyngitis, called strep throat)


Cellulitis (infection of tissues just under the skin)

Erysipelas (a superficial form of cellulitis)

Impetigo (a skin infection)

Wound infections


Infection of heart valves (endocarditis)


Scarlet fever (no longer common)

Disorders that develop after streptococcal infections

Glomerulonephritis (kidney inflammation)

Group B

Streptococcus agalactiae

In adults, especially those with diabetes mellitus



Wound infections

In newborns

In women after delivery of a baby

Bloodstream infections

Infection of the uterus (endometritis)


Various species

Infection of heart valves (endocarditis) that have been damaged by a disorder such as a congenital heart disorder or rheumatic fever

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).

Symptoms of Strep Infections

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

  • Cellulitis: The infected skin becomes red, and the tissue under it swells, causing pain.

  • Impetigo: Usually, scabby, yellow-crusted sores form.

  • Necrotizing fasciitis: The connective tissue that covers muscle (fascia) is infected. People have sudden chills, fever, and severe pain and tenderness in the affected area. The skin may appear normal until infection is severe.

  • Strep throat (pharyngitis): This infection usually occurs in children 5 to 15 years old. Children under 3 years old seldom get strep throat. Symptoms often appear suddenly. The throat becomes sore. Children may also have chills, fever, headache, nausea, vomiting, and a general feeling of illness (malaise). The throat is beefy red, and the tonsils are swollen, with or without patches of pus. Lymph nodes in the neck are usually enlarged and tender. However, children under 3 years old may not have these symptoms. They may have only a runny nose. If people with a sore throat have a cough, red eyes, hoarseness, diarrhea, or a stuffy nose, the cause is probably a viral infection, not a streptococcal infection.

  • Scarlet fever: A rash appears first on the face, then spreads to the trunk and limbs. The rash feels like coarse sandpaper. The rash is worse in skinfolds, such as the crease between the legs and the trunk. As the rash fades, the skin peels. Red bumps develop on the tongue, which is coated with a yellowish white film. The film then peels, and the tongue appears beefy red (strawberry tongue).

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

If untreated, streptococcal infections can lead to complications. Some complications result from spread of the infection to nearby tissue. For example, an ear infection may spread to the sinuses, causing sinusitis, or to the mastoid bone (the prominent bone behind the ear), causing mastoiditis.

Other complications involve distant organs. For example, some people develop kidney inflammation (glomerulonephritis) or rheumatic fever.

Toxic shock syndrome 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) 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.

If group A streptococci are identified, they may be tested to see which antibiotics are effective (a process called susceptibility testing).

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.

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 drugs (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.

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.

People with necrotizing fasciitis are treated in an intensive care unit (ICU). In necrotizing fasciitis, dead, infected tissue must be surgically removed.

More Information about Strep Infections

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

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