Macrolide-Resistant Strep Throat Infections Appear Common
Abstract & Commentary
Source: Martin JM, et al. Erythromycin-resistant group A Streptococci in schoolchildren in Pittsburgh. N Engl J Med 2002;346:1200-1206.
The authors of this investigation have been performing a long-term epidemiologic study of schoolchildren in a single, private elementary school in Pittsburgh. Approximately 100 children age 5-13 years have been followed for the past three years. During the school year, throat swabs were obtained routinely every two weeks and each time a child had a respiratory tract infection. The swabs were cultured and isolates tested for antibiotic susceptibility. The authors noted whether the child was symptomatic of a respiratory illness at the time the culture was obtained.
During the first two years of the study, 2200 swabs were obtained and 322 (15%) were positive for group A streptococci. All isolates were sensitive to erythromycin. During the third year of the study (October 2000 to May 2001), 1794 swabs were obtained and 318 (18%) grew group A streptococci. Of these 318 isolates, 153 (48%) were resistant to erythromycin. All were sensitive to clindamycin. Children with erythromycin-resistant infections were indistinguishable clinically from those with erythromycin-sensitive infections.
To determine if this drug-resistant infection was restricted to the single school, the authors evaluated 100 random pharyngeal group A streptococci isolates from the laboratory of a local children’s hospital. Thirty-eight percent of these isolates were erythromycin-resistant. The authors conclude that macrolide antibiotics should not be used routinely for streptococcal pharyngitis.
Commentary by David J. Karras, MD, FAAEM, FACEP
Both penicillin and macrolide antibiotics have been regarded as acceptable therapies for group A streptococcal pharyngitis for decades. Because of its convenient dosing, azithromycin has become the most commonly used alternative to penicillin in treating this common illness. Resistance to azithromycin in the United States has remained negligible over the years. Macrolide resistance has been noted, however, in Europe and the Far East during the past decade, and it was inevitable that it eventually would be noted in this country.
The fact that half of all isolates in this study were resistant to erythromycin (and presumably to azithromycin) is both surprising and disturbing. As the authors point out, throat cultures largely have been supplanted by rapid antigen testing in diagnosing pharyngitis, and this resistance pattern might have gone unnoticed for years. Empiric strep treatment with macrolides frequently would have been inadequate, and the risk of suppurative and non-suppurative complications (such as rheumatic fever) probably would have increased dramatically. Unless these authors’ findings are negated by larger surveillance studies, macrolide therapy probably should not be used empirically to treat strep throat. Despite its inconvenient dosing, penicillin should be used; clindamycin is the best alternative if penicillin is contraindicated.
Dr. Karras, Associate Professor of Emergency Medicine, Department of Emergency Medicine Temple University School of Medicine, Director of Emergency Medicine Research, Temple University Hospital, Philadelphia, PA, is on the Editorial Board of Emergency Medicine Alert.