49 Prevalence of Macrolide Resistant Group A Streptococcus (GAS).

Abstract

GAS pharyngitis is a common childhood infection. Resistance to penicillin has not been documented and penicillin V is the drug of choice unless the patient is allergic. Macrolides are an alternative choice for the penicillin allergic patient, but azithromycin is often used for convenience and palatability. Macrolide resistance appears to be increasing in the United States. A surveillance study of GAS resistance was performed to determine our local resistance rates particularly since local outbreaks of pertussis in 2004 and 2005 prompted an increase in macrolide use, which might contribute to increased resistance. 200 isolates have been collected from site A and 144/200 from site B from 10/05 - 7/06. Children's Mercy Hospital was designated as site A, and a community pediatric office, with a high rate of pertussis, as site B. Isolates were cultured, and erythromycin (EES) resistance was determined by Double disk diffusion (D-test) and E-test for MIC values. Chart review identified treatment and demographic data including: age, sex, race, and payor status. Comparisons were made between the 2 sites using confidence interval analysis. Fisher's exact test was used to compare data from previous surveillance of GAS resistance in 2002 at site A to current resistance at site A and site B. EES resistance was found in 7 (3.5%) at A, and 8 (5.6%) at B, CI range -0.66-0.025. Inducible resistance was noted in 43% and 37.5% respectively. PFGE studies for genetic clones are pending. There was no difference in age, sex, or payor status between site A and B with median age of 6 yearrs (range 1 to 17), 54% male, and >50% Medicaid recipients. An AA predominance was found at site A, 47% vs 8.3 % at site B. There was no difference in treatment choice between the 2 groups, with 87-90% receiving PCN or amoxicillin. A previous surveillance study of 100 isolates in 2002 revealed no resistance at site A. A statistically significant difference in comparison with current site B data, p<0.023 was found, and a suggestive trend of resistance was noted at site A, p= 0.058. Macrolide resistance appears to be increasing in our community. This was most apparent at a site where local macrolide use may have been higher but an increase was noted for both sites. Continued surveillance may impact future antimicrobial treatment decisions.