This test is used to determine whether a patient has pharyngitis that is due to a group A streptococcal infection.

Most sore throats are caused by a virus and may resolve without therapy within a few days. The bacteria group A streptococci cause pharyngitis in 5-15% of adults and 15-30% of children. It is important that these strep infections be promptly identified and treated with antibiotics. Strep throat is contagious and can spread to close contacts. If the infection is not treated, secondary complications may develop, such as rheumatic fever (which can damage the heart) and glomerulonephritis (which affects the kidneys). Because streptococcal infections are routinely diagnosed and treated, these complications have become much more rare in the United States, but they do still occur.

A rapid strep test and/or a throat culture can be used to diagnose group A streptococci as the cause of your sore throat and allow your doctor to prescribe the proper antibiotics for treatment.

If results of the rapid test, which takes 10 - 20 minutes, are positive, further testing is not needed and your doctor will start you on antibiotic therapy. If the rapid strep test is negative, a culture to grow the bacteria should be done to confirm the results. A throat culture is more accurate than the rapid strep test, but it may take several days to get results.

Your doctor will typically order this test if you have a sore throat and a fever that might be due to an upper respiratory infection. Symptoms vary and may include:

• sore throat
• fever
• headache
• tonsils that appear red with white or yellow spots at the back of the throat
• a swollen, tender neck
• weakness
• loss of appetite

A positive throat culture or rapid strep test indicates the presence of group A streptococci, the bacteria that cause strep throat. A negative rapid test indicates that you probably do not have strep throat, but the possibility cannot be ruled out until the laboratory performs a culture. Note that recent antibiotic therapy or gargling with some mouthwashes may affect test results.

Strep throat spreads from person-to-person through contact with respiratory secretions that contain the streptococcal bacteria. During flu season, the early symptoms of influenza (fever, chills, headache, sore throat, muscle pain) may mimic strep throat. Rarely, these same symptoms may be due to a more serious acute illness, septicemia. To differentiate between strep and the flu, a rapid strep test and a rapid influenza test may both be done. If both tests are negative and the clinical signs warrant it, a complete blood count (CBC) may be ordered to evaluate the patient’s white blood cells and blood cultures may be drawn to rule out sepsis. The treatment for each of these infections differs greatly and making a prompt diagnosis is imperative to starting the correct therapy.

Most patients with streptococcal pharyngitis will eventually recover without antibiotic treatment but will be contagious for a longer period of time and are at a greater risk of developing secondary complications.

Strep throat is most common in 5- to 10- year olds. Up to 20% of school children may be "carriers," persons who have the bacteria but who have no symptoms. Carriers can still spread the infection to others.