Streptococci

Streptococci

Introduction: The treatment of choice for streptococcal pharyngitis is penicillin V. yet the 5-day regimen of 1 dose of azithromycin per day is attractive and is prescribed by many practitioners, even though it is not recommended as first-line therapy for pharyngitis caused by group A streptococci. As part of an ongoing longitudinal investigation, the antimicrobial susceptibility patterns of pharyngeal isolates of group A Satreptococci were examined in schoolchildren. The sudden emergence and rapid spread of erythromycin resistance among these isolates in January 2001 were evaluated.

Methods: Surveillance throat cultures were obtained twice monthly and for every new respiratory illness in 48 children between the ages of 5 and 13 years. Seventy two children were followed up in the second year, and 100 were followed up in year 3. Forty one children participated all 3 years. Screening for resistance to erythromycin and clindamycin was initially achieved by using the Kirby-Beuer disk diffusion test. The minimal inhibitory concentration of resistant isolates was ascertained via the E test. A double disk diffusion test was used to characterize the resistance phenotype. Polymerase chain reaction was used to determine the resistance gene. The molecular relatedness of strains was ascertained via field inversion gel electrophoresis.

Results: Between October 2000 and May 2001, 1794 cultures were obtained from 100 children. Of these, 318 cultures (18%) from 60 children were positive for group A streptococci. Resistance to erythromycin was observed in 48% of these isolates (153/318), and none were resistant to clindamycin. Findings of the double disk diffusion test indicated the presence of M phenotype of erythromycin resistance. Molecular typing indicated that this outbreak was caused by a sigle strain of group A streptococci. Of 100 randomly selected isolates of group A streptococci acquired from the community between April and June 2001, 38 were resistant to erythromycin.

Conclusion: The emergence of erythromycin resistance was observed in pharyngeal isolates of group A streptococci in January 2001 during a longitudinal investigation of schoolchildren. This clonal outbreak also had an impact on the wider community.