by Dr. Moshe Ipp January 1997
As the debate continues over the best way to treat Group A Streptococcal Pharyngitis (GAS) it would appear that penicillin still reigns supreme and is the drug of choice for the treatment of GAS (except in individuals with a history of penicillin allergy).
The reason why GAS requires antibiotic treatment and the reason for using penicillin as the drug of choice include the following; Penicillin has been shown to treat acute streptococcal pharyngitis effectively, to shorten the clinical course of the disease when initiated early, to prevent suppurative complications, to prevent transmission, and to prevent the development of acute rheumatic fever. Despite the development of antibiotic resistance amongst common pediatric bacteria, GAS remains uniformly susceptible to penicillin. Penicillin has a narrow spectrum of activity and is the least expensive regimen. Penicillin may be administered intra-muscularity or orally depending on the physicians assessment of the patient's likely adherence to an oral regimen and the risks of rheumatic fever in a particular population. Broader spectrum penicillin's such as amoxicillin are known to be active against GAS and may have theoretical advantages because of higher blood levels, longer plasma half life, and lower protein binding activity. Amoxicillin may have a better compliance because of superior palatability, however, it is reported to have no microbiologic advantage over the less expensive penicillin. All patients should continue to take penicillin regularly for an entire 10 day period even though they will likely be asymptomatic after the first few days. Patients are considered non contagious 24 hours after the initiation of therapy.
What other antibiotics may be used to treat GAS?
Oral erythromycin is an acceptable alternative for patients allergic to penicillin. Erythromycin estolate, Erythromycin ethylsuccinate, Clarithromycin and Azithromycin are all effective in treating GAS. Azithromycin can be administered once a day, producing high tonsillar tissue concentrations. (500mg as a single dose on the first day, followed by 250mg once daily for 4 days) All other erythromycins should be prescribed for 10 days.
A 10 day course of an oral cephalosporin is also considered to be an acceptable alternative particularly for penicillin-allergic individuals. It is thought that narrower-spectrum cephalosporins such as cephalexin are probably preferable to the broader-spectrum cephalosporins such as cefaclor, cefuroxime, cefixime, and cefpodoxime. Although recent reports suggests that a 5 day course may be as effective as a 10 day course this is not the current recommendation at this time. The advantage of cephalosoporins in treating beta-lactamase producing upper respiratory flora which may interfere with penicillin is a theoretical consideration and remains controversial at this time. Certainly the cephalosporins are more expensive than penicillin, are associated with a higher risk of selecting resistant organisms and some forms may be more likely to produce a serum sickness-like reaction
What is considered the best way of diagnosing GAS pharyngitis?
The clinical diagnosis of GAS pharyngitis is difficult to make. The classical clinic signs suggesting streptococcal infection are tonsillar pharyngeal erythema with or without an exudate and tender anterior cervical lymphadenopathy. Other soft findings include malodorous breath, soft palate petechiae, beefy red swollen uvula, and a scarletiniform rash. The most common symptoms in individuals with GAS pharyngitis are sore throat, fever, headache, and abdominal pain especially in children. Because many of the signs and symptoms of GAS pharyngitis are non-specific it now recommended that the clinical diagnosis be confirmed with laboratory tests. Throat cultures are the conventional gold standard method for confirming the diagnosis. Rapid antigen-detection tests may be used, but since a negative test does not exclude the presence of GAS, a throat culture should be obtained in this situation. Streptococcal antibody tests (ASO titres) are of no value in the immediate diagnosis and treatment of GAS pharyngitis.
Are there signs and symptoms that would make streptococcal infection less likely?
Yes. Children who present with a sore throat and a viral like illness do not require a routine throat swab. These would include children who present with coryza hoarseness, cough, diarrhea, conjunctivitis, anterior stomatitis, and discreet ulcerative lesions. Viruses that commonly cause pharyngitis include adenoviruses, entroviruses, herpes viruses, and influenza viruses. GAS is not a common cause of pharyngitis in preschool children and in fact is unusual in children under 3 years of age and extremely rare in children under 2 years of age.
Should follow up throat cultures be performed?
No. Although no single antibiotic regimen eradicates GAS from the pharynx in 100% of treated patients by far the majority of patients will respond clinically to antibiotic treatment. The only time post-treatment throat cultures are indicated are in those individuals who remain symptomatic, those who develop recurrent symptoms, or in those who have had rheumatic fever and are at unusually high risk for recurrence.
What is the recommended treatment for those who have failed to respond to penicillin?
Many patients who appear to be treatment failures are in fact chronic carriers who have had prolonged periods of GAS colonization. Therefore, repeated courses of antibiotic treatment are not indicated in asymptomatic individuals. In symptomatic individuals who continue to have GAS in the pharynx after completion of the course of therapy, a second course, preferably with another antibiotic is recommended. Antibiotics such as amoxicillin-clavulanate, cephalosporins, and clindamycin can be used.
What are the current recommendations for treating carriers?
Chronic streptococcal carriers are defined as individuals with positive throat cultures for GAS without illness or antibody response to GAS antigens. Because it is impossible to distinguish carriers from infected individuals, all individuals who are symptomatic and are identified as having GAS by throat swab or antigen-detection tests must be treated with a course of antibiotics. Streptococcal carriers are at little risk for developing acute rheumatic fever.
References: Dajani A. Pediatrics 1995;96:4758
Anon. Can Infect Dis 1997;8:17-18.
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