Rapid Strep Test

A positive strep test needs to be treated with antibiotics.

Pharyngitis, an inflamed or sore throat, is a common symptom both in children and adults. While most are caused by virus infections, some are caused by the bacteria Streptococcus pyogenes, also known as group A streptococcus. The shorthand term is strep throat.

Strep throat is an upper respiratory infection that causes inflammation of the back of the throat and tonsils.

• Symptoms may include fever, a sore throat, pain with swallowing, white patches or pus seen at the back of the throat or on the tonsils, and swelling of the lymph nodes in the front of the neck (sometimes called swollen glands).
• Symptoms of runny nose (coryza), cough, hoarseness, and pinkeye (conjunctivitis) suggest a virus infection and not strep.li>

Strep throat usually affects children between the ages of 5 and 15, and is less common in adults. However anyone can get a strep infection and especially people who are in close contact with each other (e.g., school dorms, daycare centers, homeless shelters, military barracks) do have an increased risk of strep throat infection.

The diagnosis is important because untreated strep throat may progress to worsening infections like sinusitis, otitis media (ear infection), and meningitis. Abscesses in the back of the throat may develop in those who are not treated.

There are two severe complications of strep throat:

• Acute rheumatic fever is an autoimmune response to a strep infection, either from the throat or from a skin infection. The valves in the heart can become inflamed, as can the heart muscle and tissues surrounding the heart. Muscles, joints, skin, and the brain may also become inflamed which can lead to long-term damage.
• Post streptococcal glomerulonephritis is a rare immune complication of strep throat that affects the kidney causing inflammation and damage.

Adequate treatment of strep throat with antibiotics will prevent most cases of acute rheumatic fever. It is uncertain whether that treatment will prevent glomerulonephritis, but there may be some benefit.

The diagnosis of strep throat is made by a positive throat culture or a positive rapid strep test. These tests are done by securing throat swabs and are collected in the same way.

• The rapid strep test is done at the bedside (point of care testing) and identifies if the strep antigen is present.
• Throat culture is sent to the microbiology lab where the specimen will be grown in an incubator for 1-2 days and the group A streptococcus bacteria is identified if it grows in the culture. The throat culture is the more accurate test.

The diagnosis of strep throat cannot be made clinically. While strep throat usually doesn’t have associated cold symptoms, the physical exam is similar between strep throat and a sore throat. A health care provider won’t be able to tell the difference between the two just by looking at the patient.

Rapid strep tests for home use are available in the US, UK, and Europe, but are not FDA approved as of yet. The test is done in the same way a health care provider would at the bedside, office, clinic, or urgent care.

Over the counter strep tests are available at pharmacies and online. There are a variety of manufacturers and prices vary.

The rapid strep test is easy to perform and instructions are included in each test package. A common sequence is as follows:

• A cotton swab is wiped across the back of the throat to collect the sample, with care not to contaminate it on the tongue or other parts of the mouth.
• The swab is mixed with a reagent in a tube
• The test strip is dipped into the tube and then needs time for the results to develop
• After the appropriate wait time, the test strip is ready to be interpreted
  • There should always be a control line that becomes visible
  • If a second line becomes visible, then the test is positive and the patient has a strep infection
  • If a second line is not visible, then it is unlikely that strep is present

Look closely at the instructions provided with your individual test as there can be significant differences how individual tests are performed and interpreted.

Rapid strep tests are a reliable screening test for most patients to determine whether a strep infection is present. The sensitivity of the rapid test may be as high as 95% depending upon the manufacturer, meaning very few people with a true strep infection will have a negative test result. However, and perhaps more importantly, the specificity of the tests is very high as well (close to 98%), meaning that a negative test almost always indicates that you do not have the disease.

In the hospital, should the rapid test be negative, in a patient who is at risk for complication from a strep infection, and the health care provider has a high index of suspicion that a strep infection may still be present, a throat culture may be ordered.

A positive strep test needs to be treated with antibiotics. Depending upon a patient’s relationship with their health care provider, there may need to be a visit to get an antibiotic prescription. An alternative would be to send a picture of the positive test and have a prescription provided without a visit.

A negative test means that a strep infection is unlikely, but other significant virus infections may be present, like infectious mononucleosis (Epstein Barr virus), influenza, or infections. Depending upon how the patient feels, the severity and duration of symptoms, and any underlying medical conditions, a decision needs to be made whether to seek further care.