Erythromycin-resistant group A streptococci in schoolchildren in Pittsburgh.
BACKGROUND
Resistance to erythromycin has been very uncommon among group A streptococci in the United States.


METHODS
As part of a longitudinal study, we obtained surveillance throat cultures twice monthly and with each new respiratory tract illness from children in kindergarten through grade 8 at one school in Pittsburgh. Screening for resistance to erythromycin and clindamycin was initially accomplished with use of the Kirby-Bauer disk-diffusion test. The minimal inhibitory concentration of resistant isolates was determined by the E test. A double disk-diffusion test was used to characterize the resistance phenotype, and the polymerase-chain-reaction assay was used to identify the resistance gene. The molecular relatedness of strains was determined by field-inversion gel electrophoresis.


RESULTS
A total of 1794 throat cultures were obtained from 100 children between October 2000 and May 2001, of which 318 cultures (18 percent) from 60 of the children were positive for group A streptococci. Forty-eight percent of these isolates (153 of 318) were resistant to erythromycin. None were resistant to clindamycin. Results of the double disk-diffusion test indicated the presence of the M phenotype of erythromycin resistance. Molecular typing indicated that the outbreak was due to a single strain of group A streptococci. Of 100 randomly selected isolates of group A streptococci obtained from the community between April and June 2001, 38 were resistant to erythromycin.


CONCLUSIONS
In January 2001, during a longitudinal study of schoolchildren, we detected the emergence of erythromycin resistance in pharyngeal isolates of group A streptococci. This clonal outbreak also affected the wider community.
Martin
Judith M
JM
Department of Pediatrics, Division of Allergy, Immunology and Infectious Diseases, Children's Hospital of Pittsburgh, University of Pittsburgh School of Medicine, Pittsburgh 15213, USA. judy.martin@chp.edu
Green
Michael
M
Barbadora
Karen A
KA
Wald
Ellen R
ER
D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D002981:Clindamycin / Q000494:pharmacology / Q000627:therapeutic use; D004269:DNA, Bacterial / Q000032:analysis; D024881:Drug Resistance, Bacterial; D004917:Erythromycin / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008826:Microbial Sensitivity Tests; D010406:Penicillins / Q000627:therapeutic use; D010414:Pennsylvania; D010614:Pharynx / Q000382:microbiology; D013290:Streptococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D013297:Streptococcus pyogenes / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D010406:Penicillins; D002981:Clindamycin; D004917:Erythromycin