Throat culture

Overview
A throat culture is a laboratory diagnostic test to find a bacterial or fungal infection in the throat. A sample swabbed from the throat is put in a special cup (culture) that allows infections to grow. If an infection grows, the culture is positive. The type of infection is found using a microscope, chemical tests, or both. If no infection grows, the culture is negative.

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. See a picture of thrush in the mouth.


 * 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 health professionals 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.

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
The patient does not need to do anything before having this test. The health professional should know if the patient has recently taken any antibiotics.

How it is done
The patient will be asked to tilt her/his head back and open her/his mouth as wide as possible. The health professional will press the tongue down with a flat stick (tongue depressor) and then examine the mouth and throat. A clean swab will be rubbed over the back of the throat, around the 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, the patient 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.