Throat Culture

Test Overview

A throat culture is a test to find germs (such as bacteria or a fungus) that can cause an infection. A sample of cells from the back of your throat is added to a substance that promotes the growth of germs. If no germs grow, the culture is negative. If germs that can cause infection grow, the culture is positive. The type of germ may be identified using a microscope or chemical tests. Sometimes other tests are done to find the right medicine for treating the infection. This is called sensitivity testing.

Examples of infections that may be found during a throat culture include:

Candida albicans. This fungus causes thrush, an infection of the mouth and tongue and sometimes of the throat.
Group A streptococcus. This bacteria can cause strep throat, scarlet fever, and rheumatic fever. If strep throat is likely, a test called a rapid strep test (or quick strep) may be done before a throat culture. With a rapid strep test, results are ready in 10 minutes instead of 1 to 2 days with a throat culture. If the rapid strep test results are positive, antibiotics can be started immediately. A throat culture is more accurate than the rapid strep test. The rapid strep test can give false-negative results even when strep bacteria are present. When the results of a rapid strep test are negative, many doctors recommend doing a throat culture to make sure that strep throat is not present.
Neisseria meningitidis. This bacteria can cause meningitis.

If bacteria grows in the culture, other tests may be done to check which antibiotic will treat the infection best. This is called susceptibility or sensitivity testing.

Most sore throats are caused by an infection with a virus, such as a cold or flu. Throat cultures are not done for viral infections because it is very hard to grow viruses and it is expensive.

Why It Is Done

A throat culture may be done to:

Find the cause of a sore throat. Most sore throat infections are caused by a virus. A throat culture shows the difference between a bacterial infection and a viral infection. Finding the organism that is causing the infection can guide treatment.
Check a person who may not have any symptoms of infection but who carries bacteria that can spread to others. This person is called a carrier.

How To Prepare

You do not need to do anything before you have this test. Tell your doctor if you have recently taken any antibiotics.

How It Is Done

You will be asked to tilt your head back and open your mouth as wide as possible. Your doctor will press your tongue down with a flat stick (tongue depressor) and then examine your mouth and throat. A clean swab will be rubbed over the back of your throat, around your tonsils, and over any red areas or sores to collect a sample.

The sample may also be collected using a throat washout. For this test, you will gargle a small amount of salt water and then spit the fluid into a clean cup. This method gives a larger sample than a throat swab and may make the culture more reliable.

If your child needs a throat culture, you may hold your child on your lap while the sample is taken. This can prevent your child from moving around too much.

How It Feels

You may feel like gagging when the swab touches the back of your throat. If your throat is sore, the swabbing may be slightly painful.

Risks

Generally there is no chance of problems with collecting a sample for a throat culture. Your doctor can talk to you about any specific risks of the test.

Results

A throat culture is a test to find a bacterial or fungal infection in the throat. Throat culture test results for bacterial infections are ready in 1 to 2 days, depending on which bacteria are being tested for. Test results for a fungus may take about 7 days.

Rapid strep test results are ready in 10 to 15 minutes. This test is only for bacterial infections caused by strep bacteria.

Rapid strep test
Normal (negative results):	No strep bacteria are detected. A throat culture may be recommended.
Abnormal (positive results):	Strep bacteria are detected. This means you have strep throat. Antibiotics can be started immediately.

Throat culture
Normal (negative)	No infection (bacteria or fungi) grows in the culture.
	A negative throat culture may mean that the cause of your infection is a virus, rather than bacteria or fungus. Some viruses that cause throat infections include: Enterovirus. Epstein-Barr virus. Herpes simplex virus. Respiratory syncytial virus (RSV).
Abnormal (positive)	Bacteria grows in the culture. Some bacterial throat infections include: Strep throat. Diphtheria ( Corynebacterium diphtheriae). Whooping cough ( Bordetella pertussis).
	Fungus grows in the culture. The most common fungal throat infection is thrush, caused by the fungus Candida albicans.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

Taking antibiotics recently. This may prevent the growth of an infection in the culture.
Contamination of the throat culture sample by other types of bacteria from the mouth.
Using antiseptic mouthwashes before the culture is taken.

What To Think About

If you need to be tested for strep throat, the choice between a rapid strep test and a throat culture may not be clear. Talk to your doctor about the rapid strep test versus a throat culture.
A culture that does not grow any bacteria or fungus generally means that you either have a viral infection or that an infection is not present. Other things, such as the amount of sample, the timing of the sample, the type of culture done, and recent use of antibiotics, can prevent the growth of bacteria or fungus in the culture.
Sensitivity testing may be done to help choose the antibiotic that will best treat the bacteria causing an infection.
Some people carry bacteria but do not have symptoms of an infection. A throat culture is generally done only if the person's medical history and physical examination suggest that an infection is present.

Credits

ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Martin J. Gabica, MD - Family Medicine

Current as ofOctober 9, 2017