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 type of 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 right away. 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 type of bacteria can cause meningitis.

If bacteria grow 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 aren't done for viral infections. That's because it's very hard to grow viruses, and it's 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. This can help 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

• In general, there's nothing you have to do before this test, unless your doctor tells you to.
• 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 you can.
• Your doctor will press your tongue down with a flat stick (tongue depressor) and then examine your mouth and throat.
• A clean cotton 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. It may make the culture more reliable.

How long the test takes

The test will take less than a minute.

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

There is very little chance of having a problem from this test.

Results

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 found. A throat culture may be recommended.
Abnormal (positive results):	Strep bacteria are found. This means you have strep throat. Antibiotics can be started right away.

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 grow 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.