Resistance to Erythromycin in Group A Streptococci

BACKGROUND: The use of erythromycin in Finland nearly tripled from 1979 to 1989. In 1988, we observed an unusually high frequency of resistance to erythromycin in group A streptococci in one geographic region. Because routine testing does not detect the sensitivity of these organisms to antibiotics, we initiated a national study to evaluate the extent of this resistance. METHODS: We studied 272 isolates of group A streptococci obtained from blood cultures from 1988 through 1990. In 1990 we collected from six regional laboratories 3087 consecutive isolates from throat swabs and 1349 isolates from pus samples. Resistance was indicated by growth on blood agar containing 2 micrograms of erythromycin per milliliter after incubation in 5 percent carbon dioxide. We also evaluated the clinical importance of erythromycin resistance in a retrospective study of consecutive patients with pharyngitis. RESULTS: The frequency of resistance to erythromycin in group A streptococci from blood cultures increased from 4 percent in 1988 to 24 percent in 1990. From January to December 1990, the frequency of resistance in isolates from throat swabs increased from 7 percent to 20 percent, and resistance in isolates from pus increased from 11 percent to 31 percent. In four communities within 50 km of each other, the frequency of erythromycin resistance ranged from 2 to 5 percent to 26 to 44 percent. Several distinct DNA restriction profiles and serotypes were found among resistant isolates from the same area, suggesting a multiclonal origin. The treatment of pharyngitis with erythromycin failed in 9 of 19 patients infected with erythromycin-resistant group A streptococci, as compared with 1 of 26 patients with erythromycin-susceptible isolates (47 percent vs. 4 percent, P = 0.008). CONCLUSIONS: In Finland since 1988 there has been a rapid and substantial increase in resistance to erythromycin in group A streptococci. The extent of this resistance is particularly serious since there are only a few alternative antibiotics available for peroral treatment of group A streptococcal infections.