What is a strep A test?
Group A Streptococcus, also known as group A strep, is a type of bacteria that often lives in the nose and throat. It causes strep throat and other infections. Strep throat is an infection that affects the throat and tonsils. You can get strep throat at any age, but it's most common in children ages 5 to 15 years old.
The infection can spread from person to person through the air, for example from being close to someone who is coughing or sneezing. It can also spread when you touch something that has the bacteria on it and then touch your eyes, mouth, or nose. Another way you can get it is if you share a glass, straw, or utensils with someone who has the infection.
The infection can spread more easily among people living together or in crowded places. Some people infected with group A strep do not have symptoms or seem sick. People who are sick with strep throat are more contagious than those who do not have symptoms.
Once you have been exposed to the group A strep bacteria, it usually takes two to five days before you start to feel sick.
Strep throat can be easily treated with antibiotics. But if it's not treated, strep throat can lead to serious health problems (complications). These include rheumatic fever, a disease that can damage the heart and joints, and glomerulonephritis, a type of kidney disease.
Strep A tests check for strep A infections. There are two types of strep A tests:
- Rapid strep test. This test looks for antigens to strep A. These antigens are substances in the Strep A bacteria that trigger your immune system to fight the virus. A rapid strep test can provide results in 10-20 minutes. If a rapid test is negative, but your health care provider thinks you or your child has strep throat, they may order a throat culture.
- Throat culture. This test looks for strep A bacteria. It provides a more accurate diagnosis than a rapid test, but it can take 24-48 hours to get results.
Other names: strep throat test, throat culture, group A Streptococcus (GAS) throat culture, rapid strep test, Streptococcus pyogenes
What is it used for?
A strep A test is most often used to find out if a sore throat and other symptoms are being caused by strep throat or by a viral infection. Strep throat needs to be treated with antibiotics to prevent complications. But most sore throats are caused by viruses, and antibiotics don't work on viral infections. Viral sore throats will usually go away on their own.
Why do I need a strep A test?
Your provider may order a strep A test if you or your child has symptoms of strep throat. These include:
- A sudden and severe sore throat
- Pain or trouble swallowing
- Fever of 101 °F (38 °C) or more
- Swollen lymph nodes
- Red and swollen tonsils
- White patches or streaks of pus on the tonsils
- Tiny, red spots on the roof of the mouth, called petechiae
Some people, especially children, may have other symptoms too. Other symptoms may include:
- Headache
- Stomach pain
- Nausea or vomiting
Your provider may also order a strep A test if you or your child has a rough, red rash that starts on the face and spreads to another part of the body. This type of rash is a sign of scarlet fever, an illness that can happen a few days after you've been infected with strep A. Like strep throat, scarlet fever is easily treated with antibiotics.
If you have symptoms such as a cough or runny nose along with your sore throat, it's more likely that you have a viral infection rather than strep throat.
What happens during a strep A test?
To find out what type of illness you have, your provider will first ask about your symptoms and do a physical exam. If your provider thinks you might have strep throat, they will swab your throat to test for strep throat.
There are two types of tests for strep throat: a rapid strep test and a throat culture. Both tests are done in the same way. During the procedure:
- You will be asked to tilt your head back and open your mouth as wide as possible
- Your provider will use a tongue depressor to hold down your tongue
- They will use a special swab to take a sample from the back of your throat and tonsils
- The sample may be used to do a rapid strep test in the provider's office. Sometimes the sample is sent to a lab
- Your provider may take a second sample and send it to a lab for a throat culture if necessary.
A rapid strep test quickly shows if group A strep bacteria are causing the illness. But a throat culture takes time to see if group A strep bacteria grow from the swab. Although it takes more time, a throat culture sometimes finds infections that the rapid strep test misses. It's important to do a throat culture in children and teens since they can get rheumatic fever from an untreated strep throat infection.
Will I need to do anything to prepare for the test?
You don't need any special preparations for a rapid strep test or a throat culture.
Are there any risks to the test?
There is no risk to having swab tests, but they may cause slight discomfort and/or gagging.
What do the results mean?
If the rapid test is positive, it means you or your child has strep throat or another strep A infection. No further testing will be needed.
If the rapid test is negative but the provider thinks you or your child might have strep throat, they may order a throat culture. If you or your child has not already provided a sample, you will get another swab test.
If the throat culture is positive, it means you or your child has strep throat or other strep infection.
If the throat culture is negative, it means your symptoms are not being caused by strep A bacteria. Your provider will probably order more tests to help make a diagnosis.
If you or your child is diagnosed with strep throat, you will need to take antibiotics. Most often you will need to take them for 10 days. After a day or two of taking the medicine, you or your child should start to feel better. Most people are no longer contagious after taking antibiotics for 24 hours. But it's important to take all the medicine as prescribed. Stopping early can lead to serious complications, such as:
- Rheumatic fever
- An abscess (pocket of pus) around the tonsils or in the back of the throat
- Swollen lymph nodes in the neck
- Sinus infections
- Ear infections
People with strep throat should stay home from work, school, or daycare until they no longer have a fever and have taken antibiotics for at least 12-24 hours.
It's important to take the antibiotics as prescribed and to finish the medicine even if you start feeling better. If you stop taking them too soon, some bacteria may survive and re-infect you.
Someone who tests positive for strep throat but has no symptoms (called a "carrier") usually does not need antibiotics. They are less likely to spread the bacteria to others and very unlikely to have complications.
People can get strep throat more than once. Having strep throat does not protect someone from getting it again in the future. To prevent group A strep infections, you should:
- Cover your mouth and nose with a tissue when you cough or sneeze. Put your used tissue in the waste basket.
- If you don't have a tissue, cough or sneeze into your upper sleeve or elbow.
- Wash your hands often with soap and water for at least 20 seconds.
- If soap and water are not available, you can use an alcohol-based hand sanitizer that contains at least 60% alcohol.
- Wash glasses, utensils, and plates after they are used, especially if the person who used them is sick.
- Regularly clean and disinfect frequently touched surfaces and objects.
If you have questions about your results or your child's results, talk to your provider.
Learn more about laboratory tests, reference ranges, and understanding results.
Is there anything else I need to know about a strep A test?
Strep A can cause other infections besides strep throat. These infections are less common than strep throat but are often more serious. They include toxic shock syndrome and necrotizing fasciitis, also known as flesh-eating bacteria.
There are also other kinds of strep bacteria. These include strep B, which can cause a dangerous infection in newborns, and Streptococcus pneumoniae, which causes the most common type of pneumonia. Streptococcus pneumonia bacteria can also cause infections of the ear, sinuses, and bloodstream.
References
- ACOG: The American College of Obstetricians and Gynecologists [Internet]. Washington D.C.: American College of Obstetricians and Gynecologists; c2023. Group B Strep and Pregnancy; 2019 Jul [reviewed 2021 Jul; cited 2023 Aug 28]; [about 3 screens]. Available from: https://www.acog.org/womens-health/faqs/Group-B-Strep-and-Pregnancy
- Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Group A Streptococcal (GAS) Disease; [reviewed 2023 Mar 3; cited 2023 Aug 8]; [about 2 screens]. Available from: https://www.cdc.gov/groupastrep/index.html
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