Best Practice for the Diagnosis and Management of
Group A Streptococcus Pharyngitis

Pharyngitis is one of the most frequent reasons for patients to visit their family doctors.¹ The majority of cases of pharyngitis are not bacterial in origin; however, many (approximately half) patients receive antibiotics. Since the current level of antimicrobial use (particularly for the treatment of respiratory infections) certainly contributes to the ongoing development of resistance, physicians have an obligation to prescribe fewer antibiotics. Better management of pharyngitis is one of the mechanisms by which we can do so.

Numerous studies have demonstrated that it is not possible on clinical grounds to differentiate streptococcal from viral pharyngitis.² Although there are other causes of bacterial pharyngitis beside S. pyogenes, it is not clear that these significantly benefit from antibiotic treatment (with the obvious exception of Neisseria gonorrhoeae and diphtheria).

Overuse of antibiotics to treat respiratory infections is often attributed to our inability to differentiate bacterial from viral infections. Certainly, this is true for otitis media and in acute sinusitis. It is not the case in Group A strep where both antigen detection tests and cultures are widely available. Physicians expert in the management of infectious diseases advise treating only patients when the presence of Group A strep has been confirmed. Certainly, it is the approach advocated in the Infectious Disease Society of America Guidelines.³ At the Queen Elizabeth II HSC approximately 20% of antigen tests on kids 1-5 year olds, 35% of 5-10 year olds, 20% of 10-15 year olds and 15% of adults are positive. By treating only those infected with S. pyogenes there is a tremendous opportunity to reduce the number of antibiotics prescribed.

The Group A strep antigen detection test is almost ideal for this purpose. The test is 80-90% sensitive in detection S. pyogenes and more than 95% specific.⁴ Results can be available on the day of testing and antibiotics prescribed by the end of the day. It is recommended that negative antigen tests be confirmed by culture and that labs culturing antigen negative swabs should report most positive culture results by phone or fax on the following day.

When should you reculture? Almost never! There may be a role in patients with rheumatic fever and post-streptococcal glomerulonephritis but we almost never see these diseases any more.⁴ Some experts advocate that reculture may be useful when there appears to be "Ping-Pong" spread within a family (category B, grade III).

Recommended treatment for streptococcal pharyngitis has not changed much in the last twenty years. Penicillin V is still the recommended antibiotic. However, even the IDSA acknowledges that amoxicillin, despite its' wider spectrum is appropriate for young children. A ten day course of a penicillin or an older erythromycin preparation is still recommended, although a number of clinical trials show that five days of a newer agents is equally efficacious (e.g. clarithromycin, azithromycin, cefdinir, cefuroxime).^5-9 The problem is that the use of broader spectrum cephalosporins is more expensive and may be more prone to result in the development of resistance because of their broader spectrum of activity. Fluoroquinolones are inappropriate for streptococcal pharyngitis in any circumstance. The IDSA has developed indicators of quality patient care for patients with acute pharyngitis.⁴

How do you rank in the management of streptococcal pharyngitis? Are you doing a good job? Here are the "berries".

1. Always perform throat cultures or rapid antigen detection tests when you suspect the diagnosis.
    
2. Prescribe only after a positive result and, if already started, stop antibiotics with a negative culture report.
    
3. Prescribe only penicillin (or amoxycillin for toddlers) or, for penicillin allergic patients, erythromycin.
    
4. Don't perform follow up cultures on patients who have received an appropriate course of therapy (there are very rare exceptions e.g. rheumatic fever).
    
5. Don't perform routine throat cultures on asymptornatic family contacts.
    
6. Don't use long term prophylaxis for preventing recurring episodes of pharyngitis.

- Kevin Forward

Thanks to Dr. Leon Desormeau, Director of Laboratory Services at St. Martha's Regional Hospital in Antigonish N.S. for reviewing the draft copy of this article.

1. Bisno, A.L., Acute pharyngitis: etiology and diagnosis. Pediatrics, 1996. 97(6 Pt 2): p. 949-54.
    
2. Wannamaker, L.W., Perplexity and precision in the diagnosis of streptococcalphatyngitis. Am J Dis Child, 1972.124(3): p. 352-8.
    
3. Bisno, A.L., et al., Diagnosis and management of group A streptococcal pharyngitis: a practice guideline. Infectious Diseases Society of America [see comments]. Clin Infect Dis, 1997. 26(3): p. 574-83.
    
4. Gerber, M.A., Comparison of throat cultures and rapid strep tests for diagnosis of streptococcal pharyngitis. Pediatr Infect Dis J, 1989. 8(11): p. 820-4.
    
5. Adam, D., U. Hostalek, and K. Troster, 5-day cefixime therapy for bacterial pharyngitis andlor tonsillitis: comparison with 10-day penicillin V therapy. Cefixime Study Group. Infection, 1995. 23(Suppl 2): p. S83-6.
    
6. Aujard, Y., et aL, Comparative efficacy and safety of four-day cefuroxime axeti/ and ten-day penicillin treatment of group A betahemolytic streptococcal pharyngitis in children. Pediatr Infect Dis J, 1995.14(4): p. 295-300.
    
7. McCarty, J., J.A. Hedrick, and W.M. Gooch, Clarithromycin suspension vs penicillin V suspension in children with streptococcal phatyngitis. Adv Ther, 2000. 17(l): p. 14-26.
    
8. O'Doherty, B., Azithromycin versus penicillin V in the treatment of paediatric patients with acute streptococcal pharyngitis4onsillitis. Paediatric Azithromycin Study Group. Eur J Clin Microbiol Infect Dis, 1996. 15(9): p. 718-24.
    
9. Tack, K.J., et al., Five-day cefdinir treatment for streptococcal phafyngitis. Cefdinir Pharyngitis Study Group. Antimicrob Agents Chernother, 1998. 42(5): p. 1073-5.

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