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 Overview of Bacteria Bacteria are microscopic, single-celled organisms. They are among the earliest known life forms on earth. There are thousands of different kinds of bacteria, and they live in every conceivable... read more .)
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 Pneumococcal Infections Pneumococcal infections are caused by the gram-positive, sphere-shaped (coccal) bacteria (see figure How Bacteria Shape Up) Streptococcus pneumoniae (pneumococci). These bacteria commonly... read more ).
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 ).
Symptoms of Strep Infections
Symptoms of streptococcal infections vary, depending on where the infection is:
Cellulitis Cellulitis Cellulitis is a spreading bacterial infection of the skin and the tissues immediately beneath the skin. This infection is most often caused by streptococci or staphylococci. Redness, pain, and... read more : The infected skin becomes red, and the tissue under it swells, causing pain.
Necrotizing fasciitis Necrotizing Skin Infections Necrotizing skin infections, including necrotizing cellulitis and necrotizing fasciitis, are severe forms of cellulitis characterized by death of infected skin and tissues (necrosis). The infected... read more : 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 Throat Infection Infections of the throat and/or tonsils are common, particularly among children. Throat infections are usually caused by a virus but may be caused by bacteria such as streptococcal bacteria... read more ): 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 Sinusitis Sinusitis is inflammation of the sinuses, most commonly caused by a viral or bacterial infection or by an allergy. Some of the most common symptoms of sinusitis are pain, tenderness, nasal congestion... read more , or to the mastoid bone (the prominent bone behind the ear), causing mastoiditis Mastoiditis Mastoiditis is a bacterial infection in the mastoid process, which is the prominent bone behind the ear. Mastoiditis usually occurs when untreated or inadequately treated acute otitis media... read more .
Other complications involve distant organs. For example, some people develop kidney inflammation (glomerulonephritis Glomerulonephritis Glomerulonephritis is a disorder of glomeruli (clusters of microscopic blood vessels in the kidneys with small pores through which blood is filtered). It is characterized by body tissue swelling... read more ) or 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. This condition is a reaction... read more .
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.
Doctors suspect strep throat based on the following:
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. This condition is a reaction... read more ) 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 Testing a Microorganism's Susceptibility and Sensitivity to Antimicrobial Drugs Infectious diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites. Doctors suspect an infection based on the person's symptoms, physical examination results,... read more ).
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...
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.
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 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 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.
People with necrotizing fasciitis are treated in an intensive care unit (ICU) Types of units People who need specific types of care may be put in special care units. Intensive care units (ICUs) are for people who are seriously ill. These people include those who have had a sudden, general... read more . 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.
Centers for Disease Control and Prevention (CDC): Group A Streptococcal (GAS) Disease: Information about diseases caused by group A strep