Strep throat is caused by group A beta-hemolytic streptococcus (GAS or S. Pyogenes). Other bacteria such as non–group A beta-hemolytic streptococci and fusobacterium may also cause pharyngitis. It is spread by direct, close contact with an infected person; thus crowding, as may be found in the military and schools, increases the rate of transmission. Dried bacteria in dust are not infectious, although moist bacteria on toothbrushes or similar items can persist for up to fifteen days. Contaminated food can result in outbreaks, but this is rare. Of children with no signs or symptoms, 12% carry GAS in their pharynx, and, after treatment, approximately 15% of those remain positive, and are true "carriers".
Points Probability of Strep Management headingBody 1 or fewer <10% No antibiotic or culture needed 2 11–17% Antibiotic based on culture or RADT 3 28–35% 4 or 5 52% Empiric antibiotics.
A number of scoring systems exist to help with diagnosis; however, their use is controversial due to insufficient accuracy. The modified Centor criteria are a set of five criteria; the total score indicates the probability of a streptococcal infection.
One point is given for each of the criteria:
- Absence of a cough
- Swollen and tender cervical lymph nodes
- Temperature >38.0 °C (100.4 °F)
- Tonsillar exudate or swelling
- Age less than 15 (a point is subtracted if age >44.
A score of one may indicated no treatment or culture is needed, or it may indicate the need to perform further testing if other high risk factors exist, such as a family member having the disease.
The Infectious Disease Society of America recommends against empirical treatment and considers antibiotics only appropriate when given after a positive test. Testing is not needed in children under three as both group A strep and rheumatic fever are rare, unless a child has a sibling with the disease.
Laboratory testing => A throat culture is the gold standard for the diagnosis of streptococcal pharyngitis, with a sensitivity of 90–95%. A rapid strep test (also called rapid antigen detection testing or RADT) may also be used. While the rapid strep test is quicker, it has a lower sensitivity (70%) and statistically equal specificity (98%) as a throat culture. In areas of the world where rheumatic fever is uncommon, a negative rapid strep test is sufficient to rule out the disease.
A positive throat culture or RADT in association with symptoms establishes a positive diagnosis in those in which the diagnosis is in doubt. In adults, a negative RADT is sufficient to rule out the diagnosis. However, in children a throat culture is recommended to confirm the result. Asymptomatic individuals should not be routinely tested with a throat culture or RADT because a certain percentage of the population persistently "carries" the streptococcal bacteria in their throat without any harmful results.
As the symptoms of streptococcal pharyngitis overlap with other conditions, it can be difficult to make the diagnosis clinically. Coughing, nasal discharge, diarrhea, and red, irritated eyes in addition to fever and sore throat are more indicative of a viral sore throat than of strep throat. The presence of marked lymph node enlargement along with sore throat, fever, and tonsillar enlargement may also occur in infectious mononucleosis.
The typical signs and symptoms of streptococcal pharyngitis are a sore throat, fever of greater than 38 °C (100 °F), tonsillar exudates (pus on the tonsils), and large cervical lymph nodes.
Other symptoms include: headache, nausea and vomiting, abdominal pain, muscle pain, or a scarlatiniform rash or palatal petechiae, the latter being an uncommon but highly specific finding.
Symptoms typically begin one to three days after exposure and last seven to ten days.
Strep throat is unlikely when any of the symptoms of red eyes, hoarseness, runny nose, or mouth ulcers are present. It is also unlikely when there is no fever.
- Mouth wide open showing the throat A throat infection which on culture tested positive for group A streptococcus. Note the large tonsils with white exudate.
- Mouth wide open showing the throat Note the petechiae, or small red spots, on the soft palate. This is an uncommon but highly specific finding in streptococcal pharyngitis.
- A set of large tonsils in the back of the throat, covered in white exudate. A culture positive case of streptococcal pharyngitis with typical tonsillar exudate in an 8-year-old