Streptococcal infections are caused by any one of several species of Streptococcus.
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:
The species that cause disease 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 include group A, group B, and viridans.
Group A streptococci, as well as Streptococcus pneumoniae, are spread through inhalation of droplets of secretions from the nose or throat, dispersed when an infected person coughs or sneezes, or through 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 vary, depending on where the infection is:
Doctors suspect strep throat based on the following:
The main reason for diagnosing strep throat is to reduce the chance of developing complications, such as infection of the sinuses, middle ear, or mastoid bone or rheumatic fever, by using antibiotics. However, because symptoms of group A strep throat are often similar to those of throat infection due to a virus, testing with a throat culture or another test is necessary to confirm the diagnosis. 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).
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.
Strep throat usually resolves within 1 to 2 weeks, even without treatment. Antibiotics reduce the severity of symptoms but shorten their duration by only about 1 day. 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 need not be started immediately. Waiting up to 9 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. Usually, the bacteria that cause strep throat are not 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. Neither bed rest nor isolation is necessary.
Serious streptococcal infections (such as necrotizing fasciitis, endocarditis, and severe cellulitis) require penicillin, given intravenously, sometimes with other antibiotics. In necrotizing fasciitis, dead, infected tissue must be surgically removed.
Last full review/revision September 2008 by Matthew E. Levison, MD