Antimicrobial Non-Sensitivity Trends Among Invasive Group A and Group B Streptococcus Isolates In New York State

BACKGROUND:   Knowledge of antimicrobial non-sensitivity patterns is important for treatment decisions.  Limited access to clinical laboratory testing results and lack of standardization hinder the systematic evaluation of regional trends. Non-sensitivity patterns from active, population based surveillance have been found to successfully estimate regional trends.

METHODS:   The New York State Emerging Infections Program Active Bacterial Core surveillance conducts active, population based surveillance in 15 counties.  Isolates from invasive cases of Group A Streptococcus (GAS) and Group B Streptococcus (GBS) are sent to the state’s public health laboratory and then forwarded to CDC for typing and antimicrobial sensitivity testing.  Isolates are tested for sensitivity to ampicillin, cefotaxime, clindamycin, erythromycin, levofloxacin, penicillin, tetracycline, and vancomycin. Results from 1999 to 2011 were analyzed along with corresponding case-patient clinical information.  Isolates were identified as sensitive or non-sensitive (intermediate resistant or resistant) based on 2011 Clinical and Laboratory Standards Institute minimum inhibitory concentration value breakpoints.  Multiple drug non-sensitivity was defined as non-sensitive to two or more antimicrobials. 

RESULTS:   Over the 13 year period, all 634 GAS and 161 GBS isolates tested were sensitive to ampicillin, penicillin, cefotaxime, and vancomycin.  Over the 13 year period, non-sensitivity was highest for tetracycline (6.7-12.3% for GAS and 71.4-100.0% for GBS).  GAS non-sensitivity ranged from 1.9-10.5% for erythromycin and 0-6.8% for clindamycin.  GAS clindamycin non-sensitivity significantly increased (p=0.01) from 1999 to 2011. GBS non-sensitivity ranged from 14.3-60.0% for erythromycin and 10.0-40.0% for clindamycin.  No significant associations between multiple drug non-sensitivity and age, residence, or race were found.  GAS emm type 73 had a significantly greater odds (OR=4.04, 95% CI: 1.32-12.44) and emmtype 1 had a significantly lower odds (OR=0.13, 95% CI: 0.03-0.55) of multiple drug non-sensitivity, compared to all other types.  Type III GBS isolates had a significantly lower odds (OR=0.44, 95% CI: 0.24-0.79) of multiple drug non-sensitivity. 

CONCLUSIONS:   Antimicrobial non-sensitivity findings in this study are consistent with other published results.  All isolates were sensitive to first-line therapy (ampicillin, penicillin), therapy for penicillin allergic patients (cephalosporins), and last line therapy (vancomycin).  Non-sensitivity was common in therapies for beta-lactam allergic patients, supporting the recommendation to perform sensitivity testing for this sub-population.  The results also support the recommendation to not use tetracycline due to high resistance.  Drug non-sensitivity was not related to demographics; however, it was related to microbiological characteristics (e.g., emm type), which can help inform vaccine development.  Antimicrobial sensitivity monitoring should be continued to guide future treatment recommendations.