To diagnose a possible bacterial infection of the throat (usually Streptococcus pyogenes)
Throat Infection Test
If you have a sore throat and fever and your doctor thinks it may have a bacterial cause (although most sore throats are caused by viruses and won't require antibiotics)
The bacteria are tested for by throat culture. Your doctor may use a tongue depressor to hold down your tongue, and then insert a special swab into your mouth and brush it against your throat and tonsils. The swab will be sent to a laboratory, where culture is performed.
No test preparation is needed. The test should be performed before antibiotics are prescribed.
The test identifies Streptococcus pyogenes, known as Group A streptococcus, which are bacteria that infect the back of the throat and are a common cause for an infected and sore throat. Whilst group A Streptococcus is the commonest bacterial cause of a severe sore throat (pharyngitis), it is not the only bacterial cause and others include group C and G Streptococcus and Arcanobacterium.
How is it used?
The majority of sore throats are caused by a virus and do not require active treatment with antibiotics. Some, caused by the Streptococcus pyogenes bacterium, may be severe and are treatable with antibiotics. Your doctor will assess you based on your symptoms and may take a throat culture to help make the correct diagnosis if they think you might have a bacterial infection of your throat. This allows your doctor to prescribe the correct antibiotics for treatment. A throat culture may take several days to provide results.
When is it requested?
Your doctor may request this test if you have a sore throat and a fever that might be due to a bacterial infection. Other symptoms include:
- tonsils that may appear red with white or yellow spots at the back of the throat
- a swollen, tender neck
- skin rash
- loss of appetite, feeling sick
- flu-like illness, aching body
What does the test result mean?
Is there anything else I should know?
A sore throat due to a bacterial infection may spread through person-to-person contact. Symptoms usually occur within two to seven days after exposure. If untreated, this throat infection can create serious lifelong problems in a small minority of patients, however these complications are very rare in the UK.
This infection is most common in 5- to 15-year-olds. Up to 20% of school children may be "carriers" - people who have the bacteria but who have no symptoms. Carriers can still spread the infection to others.
How long does treatment for bacterial infection of the throat usually last?
How long should I stay away from other people if I have a positive test result?
When can my child go back to school?
If one child in my family has sore throat, is everyone going to get sick?
What is an ASO test and how is it used to detect a bacterial infection of the throat?
Antistreptolysin O (ASO) titre is a blood test used to help diagnose a current or past infection with Group A strep (Streptococcus pyogenes). It detects antibodies to streptolysin O, one of the many streptococcus antigens. This test is rarely used now compared to thirty years ago. For an acute throat infection, this test is not performed; the throat culture is used. It is because ASO may take at least a week to become positive after the infection. However, if a doctor is trying to find out if someone had a recent infection that may not have been diagnosed, this test could be helpful. In addition, it may be used to help diagnose rheumatic fever, which occurs weeks after a bacterial throat infection when the throat culture would no longer be positive.