Throat swab culture

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Throat swab culture is a laboratory test to isolate and identify organisms which may cause infections in the throat or tonsils.

Why is it done?

Sore throats are common, and most are courtesy of a virus. A sore throat may be caused by a variety of organisms (including viruses), and are usually uncomplicated and self-limiting. However, those caused by group A beta-hemolytic streptococcus (GAS) may have serious health repercussions, such as acute rheumatic fever (causing damage to heart valves), toxic shock syndrome and acute glomerulonephritis.

In a patient suspected of having a GAS pharyngitis (also known as strep throat), throat swab culture can confirm the diagnosis. From here, with quick antibiotic treatment, you can be on your way to a healthy state again.

How is the test done?

Throat swab specimens must be taken before antibiotics are started. Tell your doctor if you have taken antibiotics recently.

Sterile swabs which look like giant earbuds are used. The patient opens his mouth wide, and the swab is rubbed against the back of the throat, near to and on the tonsils. The swab is replaced in its container and immediately sent to the laboratory for incubation and culture.

Apart from identifying a bacterium, the laboratory also does an antibiogram. Here, the bug is exposed to different antibiotics to gauge its sensitivity to the specific antibiotic. In this way, the correct antibiotic can be recommended, rather than using a trial and error method.

Identifying an organism may take 24-48 hours, and a complete antibiogram up to four days.

Risks of the test

The only serious risk is that of gagging, or vomiting, induced by the swab touching the back of the throat.

What do the results mean?

The throat is not a sterile area, and is normally inhabited by a number of bacteria. Finding any one of these on swab culture does not necessarily mean it's the cause of the clinical condition of the patient. Some people are GAS carriers (meaning that the GAS lives in their throats all the time), and may have a viral throat causing the symptoms.

The most common cause of sore throat is a virus, which is not detected on this test, and for which there is no curative treatment anyway. Several other bacteria are known to cause pharyngitis:

  • Neisseria gonorrhoea (gonorrhoea bug).
  • Bordatella pertussis (whooping cough bug).
  • Corynebacterium diphtheriae ( diphtheria bug).
  • Chlamydia and mycoplasma.

The throat swab is an added diagnostic tool in a patient who is already suspected of having a strep throat, using a 9-point scoring system.

Once the swab has been taken, the patient may be given an antibiotic. If the lab report later shows the bug insensitive to the treatment, a different one can be started. If the bug is sensitive to the treatment, then valuable days will not have been lost while waiting for the result.

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