Pharyngitis is the major concern for greater than 15 million annual visits to primary care physicians in the United States. Although group A Streptococcus (GAS) is the most common bacterial cause of acute pharyngitis, only 20%-30% of school-age children and only 5%-15% of adults who present to a physician with a sore throat will turn out to have GAS pharyngitis. Treatment of GAS pharyngitis with antibiotics helps to avoid suppurative complications (for example, peritonsillar abscesses, cervical lymphadenitis, etc.), prevent acute rheumatic fever, improve clinical symptoms, decrease contagious transmission to close contacts of the patient, and allow for rapid resumption of normal activities. However, routine empiric treatment of patients with pharyngitis or upper respiratory tract infections with antibiotics has contributed greatly to the worsening of antimicrobial resistance among many common pathogens while failing to provide clinical benefit to patients with pharyngitis that is not caused by GAS. Nationally up to 70% of patients seen in primary care settings for a sore throat are prescribed antibiotics, despite the much lower incidence of GAS pharyngitis. The IDSA guidelines on the diagnosis and management of group A streptococcal pharyngitis provide a comprehensive evidence based statement addressing questions discussed below.
How should the diagnosis of GAS pharyngitis be established?
Dr. Neil Skolnik
Diagnosis should be made by throat swab and testing by rapid antigen detection test (RADT) and/or throat culture. Both tonsils, or tonsillar fossae, and posterior pharynx should be swabbed to provide an accurate and adequate sample. RADTs are approximately 95% specific and have a sensitivity of 70%-90%. This means that a positive rapid strep test is most likely a true positive, representing group A pharyngitis. There is no need for confirmatory culture to be performed. A negative rapid strep result, because of its lack of sensitivity, may reflect a false-negative result, meaning that there is a chance that the individual has strep even with a negative test. The likelihood of a false-negative test is highest in those with the greatest likelihood of having GAS: children or people whose clinical picture based on history, symptoms, and signs appear most likely to have strep. In children and adolescents, negative RADTs should have a throat culture performed because of the high incidence of GAS-causing pharyngitis in children, and the likelihood that a negative RADT is inaccurate. Adults with negative RADTs do not warrant additional testing as the incidence of GAS is much lower among adults than children. There is no role for using antistreptococcal antibody titers to help diagnose acute GAS pharyngitis.
Who should undergo testing for GAS pharyngitis?
GAS testing should be performed for individuals with a reasonable likelihood of their pharyngitis being caused by GAS. Testing is not indicated in patients with pharyngitis and symptoms strongly suggestive of viral infection (for example, cough, rhinorrhea, hoarseness, and oral ulcers). In children younger than 3 years old, the incidence of GAS pharyngitis is very low, and testing should be used only in patients who have other risk factors, such as a close household contact with GAS pharyngitis. While GAS causes only 5%-15% of pharyngitis cases in adults, adults with school age children and those who work around children are at an increased risk for GAS pharyngitis. The routine testing of asymptomatic household contacts of patients with GAS pharyngitis is not indicated.
What are the treatment recommendations for patients diagnosed with GAS pharyngitis?
Treatment recommendations for GAS start with narrow spectrum, inexpensive, beta-lactams. Once daily amoxicillin (50 mg/kg [max 1,000 mg]) given for 10 days has been shown to be effective for GAS pharyngitis and is now among the approved regimens. Additional regimens include 10 days of penicillin VK, 250 mg two to three times daily for children; 250 mg four times daily or 500 mg twice daily for adolescents and adults; or 10 days of amoxicillin, 25 mg/kg (max 500 mg) twice daily for adults. Treatment regimens for patients with penicillin allergy include cephalexin 20 mg/kg (max 500 mg) twice daily for 10 days; cefadroxil 30 mg/kg (max 1,000 mg) for 10 days; clindamycin 7 mg/kg per dose (max 300 mg/dose) three times daily for 10 days; or azithromycin 12 mg/kg (max 500 mg) once daily for 5 days; clarithromycin 7.5mg/kg per dose (max 250 mg/dose) twice daily for 10 days. Because of poorer evidence and broader spectrum, the IDSA does not recommended later-generation cephalosporins for the treatment of GAS pharyngitis. Some evidence suggests that because of developing macrolide resistance, 10 days of clarithromycin may be more effective treatment than the shorter 5-day course of azithromycin. Adjunctive therapy with an analgesic/antipyretic to control pain or fever is appropriate, but aspirin should be avoided in children, and corticosteroids are not recommended.