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 indicate 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 routine antibiotic 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. Differential diagnosis
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. Other conditions that may present similarly include epiglottitis, Kawasaki disease, acute retroviral syndrome, Lemierres syndrome, Ludwigs angina, peritonsillar abscess, and retropharyngeal abscess. Prevention
Tonsillectomy may be a reasonable preventive measure in those with frequent throat infections (more than three a year). However, the benefits are small and episodes typically lessen in time regardless of measures taken. Recurrent episodes of pharyngitis which test positive for GAS may also represent a person who is a chronic carrier of GAS who is getting recurrent viral infections. Treating people who have been exposed but who are without symptoms is not recommended. Treating people who are carriers of GAS is not recommended as the risk of spread and complications is low. Treatment
Untreated streptococcal pharyngitis usually resolves within a few days. Treatment with antibiotics shortens the duration of the acute illness by about 16 hours.