Strep test

What is being tested?
This test detects the bacterium Streptococcus pyogenes, also known as group A beta-haemolytic streptococcus or group A streptococcus (GAS). Group A streptococci can infect the back of the throat and cause “strep throat”, the most common bacterial cause of inflammation and pain at the back of the throat (pharyngitis).
While most sore throats are caused by viruses and clear up without treatment within a few days, 5-15% of adults and 15-30% of children have bacterial infections caused by group A streptococcus. It is important for these strep infections to be identified promptly and treated with antibiotics. Strep throat infections are contagious and can spread through close contact with affected people.
If the infection is not treated, secondary complications may develop: rheumatic fever, which can damage the heart, and glomerulonephritis, which affects the kidneys. Because strep infections are routinely diagnosed and treated, these complications are now very rare in the United States, but some cases can still occur.

The symptoms of strep throat vary and may be similar to those caused by other infections.

They may include:

• sore throat
• fever
• headache
• red (inflamed) throat with or without white or yellow patches
• swelling in the neck
• weakness
• loss of appetite

A rapid strep test and/or a throat swab culture are carried out to find the cause of these symptoms; this allows the doctor to prescribe appropriate antibiotic treatment.

How is the sample collected for testing?
A doctor, nurse or other healthcare professional uses a tongue depressor to hold the tongue down, inserts a special swab into the mouth and rubs it against the back of the throat and the tonsils.
The swab can be used for a rapid strep test in a doctor’s surgery or clinic, or it can be sent to a laboratory. A second swab may be collected at the same time as the first. This additional sample is used for a throat swab culture as a follow-up test, if needed.

Is any test preparation needed to ensure the quality of the sample?
No preparation is needed. The test must be carried out before starting antibiotic treatment.

1. How is it used?
2. When is it requested?
3. What does the test result mean?
4. Is there anything else I should know?

1. How is it used?
A rapid strep test is used to determine whether a person with a sore throat (pharyngitis) has a group A streptococcus infection.
If the results of the rapid test, which takes 10-20 minutes, are positive, no further tests are needed. If the rapid strep test is negative, a throat swab culture should be carried out to grow the bacteria in the laboratory and confirm the results.
A throat swab culture is more accurate than a rapid strep test, but it may take several days to get the results.

2. When is it requested?
A doctor usually requests this test when a person has a sore throat and other symptoms suggesting strep throat. The doctor’s suspicion may be greater if the person is a child and/or has been in close contact with someone previously diagnosed with strep throat. The symptoms of strep throat vary and may include:

• sore throat
• fever
• headache
• red (inflamed) throat with or without white or yellow patches
• swelling in the neck
• weakness
• loss of appetite

3. What does the test result mean?
A positive rapid strep test indicates the presence of group A streptococci, the bacteria that cause strep throat. A negative rapid test indicates that the person probably does not have strep throat, but the possibility cannot be ruled out until the laboratory has carried out a throat swab culture. If the throat swab culture is positive for group A streptococci, the person has a strep infection. If the swab is negative, the sore throat is more likely to be due to a viral infection that will clear up on its own.

4. Is there anything else I should know?
Strep infection spreads from person to person through contact with respiratory secretions containing streptococcus bacteria. During the flu season, the early symptoms of flu, such as fever, chills, headache, sore throat and muscle aches, can mimic strep throat. Very rarely, these same symptoms may be due to a more serious acute illness, septicaemia. To tell strep throat apart from ordinary flu, both a rapid strep test and a flu test may be carried out. If both tests are negative and the clinical picture requires it, a full blood count with differential may be carried out to assess the white blood cells and, more rarely, a blood culture to rule out sepsis.
The treatment for each of these infections is very different, and a prompt diagnosis is essential to start the right treatment.
Most people with strep throat can recover even without antibiotic treatment, but they will be contagious for longer and have a higher risk of developing secondary complications.
Strep throat is most common in children aged 5 to 10. Up to 20% of school-age children may be carriers (people who have the bacteria but no symptoms). Carriers can spread the infection to others.
Antibiotic treatment or gargling with some recent mouthwashes may affect the results of the rapid strep test

1. How long does treatment for strep throat usually last?
2. How long should I stay away from other people if my test result is positive?
3. When can my child go back to school?
4. If a child in my family has strep throat, will everyone get ill?
5. What is an ASO test and how is it used to detect a strep infection?
6. Are there other types of infection caused by group A streptococcus?

1. How long does treatment for strep throat usually last?
From 10 to 14 days, depending on the antibiotic prescribed.

2. How long should I stay away from other people if my test result is positive?
You need to complete at least 24 hours of antibiotics before being in close contact with others.

3. When can my child go back to school?
Usually after one full day of antibiotic treatment and when there is no significant fever.

4. If a child in my family has strep throat, will everyone get ill?
Other family members, including adults, can be infected by the bacteria. The doctor will usually test all family members who have a sore throat and may, in some cases, test the whole family for strep. Although antibodies may protect those who have had a previous strep infection, there are many different strains of this organism, and it is unlikely that anyone will be immune to all of them.
So someone may have repeated bouts of strep throat. The best way to reduce the risk of passing the bacteria on to others is to cover your mouth when coughing and sneezing and/or to sneeze into the crook of your arm or shoulder. After sneezing or coughing into a handkerchief or tissue, wash your hands thoroughly with soap and water or with an alcohol-based hand gel.

5. What is an ASO test and how is it used to detect a strep infection?
The ASO (antistreptolysin O) test is a blood test used to diagnose a current or past infection with group A streptococcus (Streptococcus pyogenes). It detects antibodies to streptolysin O, one of the many streptococcal antigens. This test is requested much less often today than thirty years ago.
For an acute strep infection, the ASO test is not helpful; a rapid strep test or throat culture should be used. However, if a doctor is trying to find out whether someone has had a recent strep infection that may not have been diagnosed, this test may be useful. ASO results can also be used to diagnose the cause of rheumatic fever or glomerulonephritis, which occur weeks after a strep throat infection, when the rapid strep test and throat swab culture would be negative.

6. Are there other types of infection caused by group A streptococcus?
Group A streptococcus can also cause infections that occur separately from a sore throat, such as impetigo and, more rarely, more invasive conditions such as toxic shock syndrome or necrotising fasciitis (the so-called “flesh-eating bacteria”).