December 1997
SAN FRANCISCO - New practice guidelines for the diagnosis and management of group A streptococcal pharyngitis were presented here at a recent meeting of the Infectious Diseases Society of America.
"Before we set the guidelines, we needed to determine our rationale for treating group A strep pharyngitis," said Alan L. Bisno MD, University of Miami and the VA Medical Center in Miami, chair of the committee that developed the guidelines. The rationale was:
The committee also recognized that group A streptococci (GAS) are only responsible for a minority of cases of acute pharyngitis - accounting for about 20% of cases in children. About 5% of these cases may be due to other bacteria, while another 40% to 45% are due to viruses. Approximately 5% are due to other organisms and in 30% to 40% of cases there is no etiologic diagnosis.
There is a broad overlap in the clinical signs and symptoms of acute pharyngitis caused by GAS and other agents, particularly viruses, so it is difficult to make a clinical diagnosis with adequate precision, Bisno said.
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"Group A streptococcal pharyngitis should first be suspected on clinical and epidemiological grounds and then supported by test results," Bisno said. "The test could either be a positive throat culture or a positive rapid antigen detection test. However, a negative rapid test should be confirmed with a throat culture, because studies have shown that rapid tests are somewhat less sensitive than throat cultures in detecting streptococci in the posterior pharynx."
Although recent reports on the new assays show that they have high sensitivities in preliminary studies, the committee felt that more data was needed before it could recommend their use without a throat culture confirmation.
"Most of the rapid tests when they first come out have reports of extremely good sensitivity - 95% to 97% - but the more they're studied in general clinical practice, the more likely it is that the sensitivity is 80% or less, Bisno said.
"Once GAS pharyngitis is diagnosed, the patient should receive therapy with an antimicrobial agent for a duration that is likely to eradicate the infecting organism," Bisno said. Penicillin V is the drug of choice, based on its narrow spectrum of antimicrobial activity, its safety profile and its modest cost.
The dosage for children is 250 mg given two or three times daily for 10 days. If there is a question of compliance, benzathine penicillin G in a single injection of 0.6 million units for children less than 60 lbs and 1.2 million units for larger children is an adequate treatment.
For penicillin-allergic patients, the treatment choices are erythromycin estolate at 20 mg/kg/day to 40 mg/kg/day, divided into two or three doses; or erythromycin ethylsuccinate at 40 mg/kg/day, divided into two or three doses for 10 days.
First- and second-generation cephalosporins like clarithromycin (Biaxin, Abbott) and azithromycin (Zithromax, Pfizer) are also effective, but are not recommended by the committee. Its recommendations coincided with those of the American Heart Association and the American Academy of Pediatrics. All three groups recommended penicillin as the first-line treatment for GAS pharyngitis, with erythromycin as the choice for penicillin-allergic patients.
The type of antimicrobial therapy used to treat GAS is a controversial issue among physicians, as is the treatment duration. There have been a number of studies on short courses of cephalosporins and macrolides, indicating that they can eradicate GAS in fewer than 10 days, Bisno said. However, the committee did not feel, based on the evidence available, that it could recommend these shorter courses. It was particularly concerned with the use of broader spectrum agents in light of growing antibiotic resistance of various organisms.
"What I want to remind you of is that when macrolide usage becomes very prevalent, the resistance of GAS to macrolides increases dramatically," Bisno said, adding that this fact was proven in Japan 10-15 years ago and more recently in Finland.
Currently, macrolide resistance in the United States is a rare phenomenon; occurring only in about 5% of all GAS isolates. This, however, could change if U.S. physicians increase their use of macrolides.
A third controversial issue that Bisno discussed was the culture and treatment of contacts of patients with invasive disease. He said that with rare exceptions it is not necessary to culture the throats or treat asymptomatic household contacts. These rare exceptions might include families where there is a history or a presence of rheumatic fever, or if there is an outbreak of rheumatic fever or glomerulonephritis.
When multiple episodes of pharyngitis occur over months or years it can be difficult to differentiate viral infections in a streptococcal carrier from true GAS infections, Bisno said.
For more information:
- Bisno AL. Diagnosis and management of group A streptococcal pharyngitis: a practice guideline. Presented at the Infectious Diseases Society of America 35th Annual Meeting. Sept. 13-16. San Francisco.
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[Search]Copyright 1997, SLACK Incorporated. Revised 12 February 1998.