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Avoid overtreatment: are clinical criteria enough to dx adult strep?

NEW YORK -- Clinical criteria alone are inadequate for the diagnosis of group A streptococcal pharyngitis in adults. Dr. Alan L. Bisno said at a meeting on infectious disease sponsored by the Center for Bio-Medical Communication.

The goal of the management of acute pharyngitis in adults in primary care should be to identify patients requiring specific diagnosis and therapy and to avoid unnecessary and potentially deleterious therapy in the rest, said Dr. Bisno, chief, medical service, Miami Veterans Affairs Medical Center.

Group A streptococcus is the only commonly occurring bacterial pharyngeal pathogen for which antimicrobial therapy is required, he said.

In the estimated 6.7 million annual doctor visits in the United States by adults with sore throat between 1989 and 1999, antibiotics were prescribed in 73%--yet only 10% of the infections were streptococcal.

Dr. Bisno therefore takes "strong exception" to the guidelines for treating acute pharyngitis in adults endorsed by the Centers for Disease Control and Prevention, the American College of Physicians, and the American Academy of Family Physicians (Ann. Intern. Med. 134[6]:506-08, 2001).

The CDC-ACP-AAFP recommendations are based on the Centor criteria. (See box.) Two options are offered. The first option is empiric treatment for patients with three or four Centor criteria and no treatment for all others. The second option is empiric treatment of all patients with four criteria, rapid antigen detection testing of those with three (or possibly two), and treatment of those who are positive.

But all published algorithms, including Centor's, are more reliable for ruling out strep throat than for identifying patients who should be treated, Dr. Bisno said. "In Centor's original data, for patients who had all four criteria present, which occurred in only 10% of 100, the positive predictive value was 56%," he said. "One way of looking at that is to say if your patient has all four criteria the chances of his having strep throat are little better than flipping a coin," he said. And for patients with three criteria, which was the case in 20%, the positive predictive value went down to 32%.

"So for the 30% of patients who come in with three or four Centor criteria, which are the ones the CDC and the ACP say you can treat empirically, actually only 40% of them would have had strep throat," he said. "And this is in a guideline whose stated purpose is to decrease unnecessary antimicrobial use. The endorsement of even limited empiric treatment by the ACP and the CDC may be the death knell of the throat culture or even the rapid test."

"I want to point out that, although it's not clear in the published guidelines, the [CDC-ACP-AAFP] approach is specifically not endorsed by the Infectious Disease Society of America," Dr. Bisno added. Rather, the IDSA has formulated its own guidelines on the diagnosis and treatment of pharyngitis, with Dr. Bisno as first author (Clin. Infect. Dis. 35[2]:113-25, 2002). These state, "The diagnosis should be suspected on clinical and epidemiological grounds and then supported by performance of a laboratory test."

The IDSA committee's recommendation was based on these assumptions:

* The prevalence of group A strep in adults is low, at 5%-15%.

* The risk of a first attack of rheumatic fever in an adult is extraordinarily low (except in Salt Lake City).

* Treatment offers only modest symptomatic benefit.

* The main objective should be to avoid unnecessary antimicrobial prescriptions in the 90% of adults with pharyngitis who do not have strep throat.

The IDSA also suggests not testing adult patients at low risk and for rapid tests to be used without culture backup.

With regard to treatment, penicillin remains the drug of choice for streptococcal pharyngitis because it is safe, effective, and inexpensive; has a narrow spectrum of effect; and raises no concerns about resistance. "There has never been a group A streptococcus in the history of the world recovered from clinical sources that was resistant to penicillin." Dr. Bisno commented.

There has been much discussion in the literature about the use of cephalosporins in preference to penicillin, on the basis of statements that penicillin has become less effective in the eradication of group A streptococci in the pharynx than it was in past years. "That is simply not true," Dr. Bisno said. "In carefully selected, high quality studies, [penicillin's effectiveness] is no different than it was 20 or 30 years ago."

As to cost, the average wholesale price to the pharmacist for 5 days' treatment with a broad-spectrum cephalosporin such as cefpodoxime is about $47, while the price tag for 10 days of treatment with erythromycin or penicillin is just over $9. "You can have your $10 treatment or your $50 treatment," Dr. Bisno said.

RELATED ARTICLE: The Centor Criteria

In 1981, Dr. R.M. Centor proposed these criteria for the diagnosis of group A streptococcal pharyngitis:

* Presence of tonsillar exudates.

* Swollen, tender anterior cervical nodes.

* Absence of cough.

* History of fever.

Source: Med. Decis, Making 1(3):239-46, 1981


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Title Annotation:Infectious Diseases
Author:Walsh, Nancy
Publication:Internal Medicine News
Date:May 1, 2004
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