High Incidence of Erythromycin-ResistantStreptococcus pyogenesin Monza (North Italy) in Untreated Children With Symptoms of Acute Pharyngo-Tonsillitis: An Epidemiological and Molecular Study

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Abstract
A retrospective analysis of susceptibility data available for Group A streptococcal isolates collected between January 1990 and January 1996 at the Hospital Microbiology Laboratory of Monza (North Italy), showed a sharp rise in the erythromycin resistance rates during the last 3 years. Streptococcus pyogenes resistant to erythromycin accounted for approximately 1% of strains isolated between 1990 and 1992; the percentage then rose from 5% in 1993 to almost 39% in 1995. In January 1996, the resistance rates peaked to 81%. A prospective controlled study performed between March and May of 1996 to determine the percentage of erythromycin-resistant Group A streptococci isolated in Monza from untreated children with acute pharyngo–tonsillitis, gave further confirmation of a high rate of erythromycin resistance (47%) in this area. Molecular characterization by T-serotyping and pulse-field gel electrophoresis analysis of 25 erythromycinresistant Group A streptococcal isolates, showed a relatively high degree of heterogeneity among these strains, demonstrating that the increased resistance is not caused by the spread of a single clone.