Strep throat is caused by group A beta-hemolytic streptococcus (GAS or S. pyogenes).[11] Other bacteria such as non–group A beta-hemolytic streptococci and fusobacterium may also cause pharyngitis.[8][10] 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.[10][12] Dried bacteria in dust are not infectious, although moist bacteria on toothbrushes or similar items can persist for up to fifteen days.[10] Contaminated food can result in outbreaks, but this is rare.[10] Of children with no signs or symptoms, 12% carry GAS in their pharynx,[5] and, after treatment, approximately 15% of those remain positive, and are true "carriers".[13]
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.[14] The modified Centor criteria are a set of five criteria; the total score indicates the probability of a streptococcal infection.[8]
One point is given for each of the criteria:[8]
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.[8]
The Infectious Disease Society of America recommends against empirical treatment and considers antibiotics only appropriate when given after a positive test.[6] 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.[6]
Laboratory testing => A throat culture is the gold standard[15] for the diagnosis of streptococcal pharyngitis, with a sensitivity of 90–95%.[8] 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.[8] In areas of the world where rheumatic fever is uncommon, a negative rapid strep test is sufficient to rule out the disease.[16]
A positive throat culture or RADT in association with symptoms establishes a positive diagnosis in those in which the diagnosis is in doubt.[17] In adults, a negative RADT is sufficient to rule out the diagnosis. However, in children a throat culture is recommended to confirm the result.[6] 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.[17]
As the symptoms of streptococcal pharyngitis overlap with other conditions, it can be difficult to make the diagnosis clinically.[8] 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.[8] The presence of marked lymph node enlargement along with sore throat, fever, and tonsillar enlargement may also occur in infectious mononucleosis.[18]
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.[8]
Other symptoms include: headache, nausea and vomiting, abdominal pain,[9] muscle pain,[10] or a scarlatiniform rash or palatal petechiae, the latter being an uncommon but highly specific finding.[8]
Symptoms typically begin one to three days after exposure and last seven to ten days.[3][8]
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.[6]
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.[8]&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