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Throat culture
Culture, throat
Rapid strep test
Nome formal
Group A streptococcus; Group A beta hemolytic streptococcus
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Este artigo foi modificado pela última vez em 10 de Julho de 2017.
At a Glance
Why Get Tested?
To determine if a sore throat is "strep throat" that is caused by group A streptococcus (GAS)
When To Get Tested?
When you have a sore throat that your doctor thinks may be due to a bacterial infection
Sample Required?
A swab rubbed against the back of your throat and tonsils
Test Preparation Needed?
What is being tested?
This test identifies the presence of the bacteria Streptococcus pyogenes, also known as group A beta-hemolytic streptococcus and group A streptococcus (GAS). Group A streptococci can infect the back of the throat and cause “strep throat,” the most common bacterial cause of inflammation and soreness of the back of the throat (pharyngitis).

While most sore throats are caused by a virus and will resolve without treatment within a few days, 5-15% of adults and 15-30% of children have bacterial infections caused by this bacteria. It is important that these strep infections be promptly identified and treated with antibiotics. Strep throat is contagious and can spread to close contacts. If the infection is not treated, secondary complications may develop, such as rheumatic fever, which can damage the heart, and glomerulonephritis, which affects the kidneys. Because streptococcal infections are routinely diagnosed and treated, these complications have become much rarer in the United States, but they do still occur.

Symptoms of strep throat vary and can be similar to those caused by other infections. They may include:

  • Sore throat
  • Fever
  • Headache
  • Reddened (inflamed) throat with or without white or yellow spots
  • A swollen, tender neck
  • Weakness
  • Loss of appetite

A rapid strep test and/or a throat culture is used to diagnose group A streptococci as the cause of these symptoms and allows the doctor to prescribe the proper antibiotics for treatment.

How is the sample collected for testing?

A doctor, nurse, or other health care professional uses a tongue depressor to hold down your tongue and then inserts a special swab into your mouth and rubs it against the back of the throat and tonsils. The swab may be used to do a rapid strep test in a doctor’s office or clinic, or it may be sent to a laboratory. A second swab may be collected along with the first one. This extra sample is used to perform a throat culture as a follow-up test when necessary.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed. The test should be performed before antibiotics are prescribed.
Accordion Title
Common Questions
  • How is it used?
    A rapid strep test is used to determine whether a person with a sore throat (pharyngitis) has a group A streptococcal infection.

    If the results of the rapid test, which takes 10 - 20 minutes, are positive, further testing is not needed. If the rapid strep test is negative, a throat culture should be performed to grow the bacteria in the laboratory and confirm the results. A throat culture is more accurate than the rapid strep test, but it may take several days to get results.

  • When is it ordered?
    A doctor will typically order this test when a person has a sore throat and other symptoms that suggest strep throat. He will have a higher suspicion of strep when the affected person is a child and/or if the person has been in close contact with someone who has been diagnosed with strep throat. Symptoms of strep throat vary and may include:
    • sore throat
    • fever
    • headache
    • reddened (inflamed) throat with or without white or yellow spots
    • a swollen, tender neck
    • weakness
    • loss of appetite
  • What does the test result mean?
    A positive rapid strep test indicates the presence of group A streptococci, the bacteria that cause strep throat. A negative rapid test indicates that the affected person probably does not have strep throat, but the possibility cannot be ruled out until the laboratory performs a throat culture. If the throat culture is positive for group A streptococci, then the person tested does have strep throat. If it is negative, then it is most likely that the sore throat is due to a viral infection that will resolve on its own.
  • Is there anything else I should know?
    Strep throat spreads from person-to-person through contact with respiratory secretions that contain the streptococcal bacteria. During influenza season, the early symptoms of influenza, such as fever, chills, headache, sore throat, muscle pain, may mimic strep throat. Very rarely, these same symptoms may be due to a more serious acute illness, septicemia. To differentiate between strep and influenza, a rapid strep test and a rapid influenza test may both be done. If both tests are negative and the clinical signs warrant it, a complete blood count (CBC) may be ordered to evaluate the person's white blood cells and, rarely, blood cultures may be drawn to rule out sepsis. The treatment for each of these infections differs greatly and making a prompt diagnosis is imperative to starting the correct therapy.

    Most people with streptococcal pharyngitis would eventually recover without antibiotic treatment, but they will be contagious for a longer period of time and are at a greater risk of developing secondary complications.

    Strep throat is most common in 5- to 10- year olds. Up to 20% of school children may be "carriers," persons who have the bacteria but who have no symptoms. Carriers can still spread the infection to others.

    Recent antibiotic therapy or gargling with some mouthwashes may affect the rapid strep test results.

  • How long does treatment for strep throat usually last?
    Ten to 14 days, depending on the antibiotic prescribed.
  • How long should I stay away from other people if I have a positive test result?
    You should complete at least 24 hours of antibiotics before close contact with others.
  • When can my child go back to school?
    Usually after one full day of therapy and absence of significant fever.
  • If one child in my family has strep throat, is everyone going to get sick?
    Other family members, including adults, can be infected by the bacteria. The doctor will usually test all family members who have sore throats and may, in some instances, want to test the whole family for strep throat. Although antibodies may protect those who have had previous strep infections, there are so many different strains of this organism that being immune to all of them is unlikely. Therefore, someone could potentially get strep throat again and again. The best way to decrease the risk of transmission of the bacteria to others is to cover coughs and sneezes by coughing and/or sneezing into the bend of your arm or shoulder. After sneezing or coughing into a tissue or handkerchief, wash hands thoroughly with soap and water or alcohol-based hand scrub.
  • What is an ASO test and how is it used to detect a strep infection?
    Antistreptolysin O (ASO) is a blood test used to help diagnose a current or past infection with group A strep (Streptococcus pyogenes). It detects antibodies to streptolysin O, one of the many strep antigens. This test is rarely ordered now compared to thirty years ago. For an acute strep throat infection, the ASO test is not helpful; the rapid strep test or throat culture should be used. However, if a doctor is trying to find out if someone had a recent strep infection that may not have been diagnosed, this test could be helpful. In addition, it may be used to help diagnose rheumatic fever or glomerulonephritis, which occurs weeks after a strep throat infection when the rapid strep and throat culture would no longer be positive.
  • Do other group A streptococous infections occur?
    Group A streptococcus can also cause infections that occur separately from strep throat, such as impetigo and, rarely, more invasive conditions such as toxic shock syndrome or necrotizing fasciitis (the so-called “flesh-eating bacteria”).
View Sources
Sources Used in Current Review

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 912-913.

Forbes, B. et. al. (© 2007). Bailey & Scott’s Diagnostic Microbiology, 12th Edition: Mosby Elsevier Press, St. Louis, MO. Pp 265-278.

Smith, D. S. (Updated 2008 September 3). Streptococcal screen. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003745.htm. Accessed May 2009.

Sharif, I. (2008 November). Strep Throat. TeensHealth, The Nemours Foundation [On-line information]. Available online at http://kidshealth.org/teen/infections/bacterial_viral/strep_throat.html# through http://kidshealth.org. Accessed May 2009.

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Vorvick, L. (Updated 2009 March 14). Strep throat. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000639.htm. Accessed May 2009.

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Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

(2005 October 11). Group A Streptococcal (GAS) Disease (strep throat, necrotizing fasciitis, impetigo). CDC, Division of Bacterial and Mycotic Diseases [On-line information]. Available online at http://www.cdc.gov/ncidod/dbmd/diseaseinfo/groupastreptococcal_g.htm through http://www.cdc.gov.

Vincent, M., et. al. (2004 March 15). Pharyngitis. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20040315/1465.html through http://www.aafp.org.

Kazzi, A. and Wills, J. (2005 April 21, Updated). Pharyngitis. eMedicine [On-line information]. Available online at http://www.emedicine.com/emerg/topic419.htm through http://www.emedicine.com.

Gerber, M. and Shulman, S. (2004 July). Rapid Diagnosis of Pharyngitis Caused by Group A Streptococci. Clinical Microbiology Reviews, July 2004, p. 571-580, Vol. 17, No. 3 [On-line journal]. Available online at http://cmr.asm.org/cgi/content/full/17/3/571 through http://cmr.asm.org.

Homeier, B. (2005 September, Reviewed). Strep Throat. KidsHealth for Parents, Nemours Foundation [On-line information]. Available online at http://kidshealth.org/parent/infections/lung/strep_throat.html through http://kidshealth.org.