Strep

Streptococci are subdivided into five main pathogenic groups commonly found in humans (A, B, C, D and G). This subdivision is based on the antigenic differences of the carbohydrates in the bacterial cell wall. Group A Streptococci (GAS) contain one species, Streptococcus pyogenes. Group B Streptococci contain one species, Streptococcus agalactiae. Groups C, D and G each contain several species.

Streptococcus pyogenes accounts for more than 90% of the disease caused by streptococci and are the most common cause of bacterial pharyngitis. Streptococcal disease is classified as either suppurative (primary infections) or nonsuppurative (complications from primary streptococcal infection). A common characteristic of suppurative diseases is the formation of pus. Suppurative diseases include pharyngitis (commonly referred to as "strep throat"), puerperal fever, impetigo, cellulites and erysipelas. Nonsuppurative diseases include scarlet fever, rheumatic fever, acute glomerulonephritis and erythema nodosum.

Streptococcal pharyngitis, or "strep throat," is a common bacterial infection found in childhood. Group A Streptococci (GAS) are responsible for the most streptococcal pharyngitis cases although other groups, such as C and G, may also cause disease. Strep throat affects all age groups but is most common in children between the ages of 5 to 15 years of age. Strep throat has an incubation period of 2-4 days. Classic symptoms include the abrupt onset of sore throat accompanied by fever, malaise and headache. Children may experience additional symptoms such as nausea, vomiting and abdominal pain. Physical findings often reveal pharyngeal erythema, enlarged tonsils with exudate and tender cervical lymphadenopathy. Viral pharyngitis may mimic streptococcal pharyngitis, but unlike strep throat, viral pharyngitis will often be accompanied by cough and rhinorrhea and cervical lymphadenopathy and pharyngeal exudates are usually absent in viral pharyngitis. The common cold, influenza, adenovirus and mononucleosis may also present with signs and symptoms pharyngitis.

Transmission

Strep throat is spread by direct person-to-person contact via nasal and salivary secretions. Crowding is a significant risk factor that increases the likelihood of disease spread.

Diagnosis

The diagnosis of strep throat is based on symptoms, physical findings and a variety of diagnostic procedures. Prompt and accurate treatment is paramount in order to prevent the occurrence of non-suppurative disease such as acute rheumatic fever and post streptococcal acute glomerulonephritis that can occur following the acute infection. The standard procedure for Group A Strep diagnosis is bacterial culture, but results may take 2-3 days. In result, physicians must either treat patients presumptively while awaiting culture results or, alternatively, withhold antibiotic therapy until the presence of Streptococcus pyogenes is confirmed with culture. Since the 1980s, commercial rapid antigen detection tests (RADTs) have been available as a means of Group A Strep detection. The advantage of rapid diagnostic tests is that they can be quickly performed in the physician’s office; however due to sensitivity limitations, supplemental testing is required for negative results. Molecular tests that detect Group A Strep DNA have recently become available. While not as rapid as the antigen test, they provide a definitive result (no supplemental testing required) while the patient is in the doctor’s office.

Treatment

Antibiotic treatment for Strep throat is recommended when children have the signs and symptoms consistent with Streptococcal pharyngitis and have a positive throat culture or rapid antigen test. Treatment can reduce the duration of symptoms and the likelihood of complications such as retropharyngeal abscess, but the primary purpose of treatment is to prevent rheumatic fever. Asymptomatic patients should not be tested and if they are tested, they should not be treated even if they test positive.

Recommended Reading

Shulman et al Clinical Infectious Diseases 2012, 55:86-102

http://www.cdc.gov/features/strepthroat/

http://www.cdc.gov/ncidod/dbmd/diseaseinfo/groupastreptococcal_g.htm