Use of PCR for Diagnosis of Group A Streptococcal Pharyngitis in the United States, 2011–2015

Background. Current susceptibility testing recommendations for β-hemolytic streptococci outline testing for clindamycin resistance, including inducible resistance by a positive D-zone phenotype. However, few studies describe the prevalence of clindamycin resistance among invasive GCS and GGS organisms. This study aims to describe the prevalence of clindamycin resistance among GCS/GGS compared with invasive group A streptococci (GAS) during the same period in a large United States health system. Methods. Streptococcus isolates from blood, tissue, and body fluids (n = 298) recorded from January 1, 2013 to May 1, 2017 were audited using SafetySurveillor® software. Members of the anginosus-group streptococci were excluded. Specimens submitted to the clinical microbiology laboratory were grown in 5% CO2 on colistin-nalidixic-acid agar, Mueller–Hinton 5% sheep blood agar, and chocolate agar. Cultures positive for β-hemolytic streptococci were identified to the species level via MALDI-TOF MS. Disk diffusion D-zone testing was performed with 0.5 McFarland standards using erythromycin (15 μg) and clindamycin (2 μg) disks 12 mm apart on Mueller–Hinton 5% sheep blood agar plates incubated at 35°C in 5% CO2 for 20–24 hours. Susceptibilities to penicillin, erythromycin, clindamycin, and vancomycin were recorded per current CLSI breakpoints. Results. A total of n = 212 GCS/GGS isolates were tested, of which n = 61 (28.8%) demonstrated clindamycin resistance; 85.2% were clindamycin resistant via a positive D-zone phenotype compared with 14.8% that were constitutively clindamycin resistant. A total of n = 86 GAS isolates were tested, of which n = 9 (10%) demonstrated clindamycin resistance; 44% reported clindamycin resistance via a positive D-zone phenotype compared with 56% which were constitutively clindamycin resistant. Conclusion. Clindamycin resistance among GCS and GGS was present in 24.5% of the isolates tested compared with 10% for GAS. As a proportion of the total number of isolates tested, inducible resistance was 14.5% more frequent among GCS and GGS than was observed for GAS. This study demonstrates a higher proportional level of clindamycin resistance in GCS/GGC compared with GAS infections detected over the same study period. Disclosures. All authors: No reported disclosures.