Emergence of Erythromycin Resistant Invasive Group A Streptococcus in West Virginia, United States

Combination therapy with penicillin and clindamycin has been a mainstay for treatment of invasive group A Streptococcus (iGAS) infections yet increasing macrolide resistance may limit such treatment for strains displaying MLSB phenotypes. The CDC recently reported erythromycin and clindamycin resistance rates for iGAS exceeding 20% in 2017. Here, we investigated 76 iGAS isolates from 66 patients identified at J.W. Ruby Memorial Hospital in West Virginia from 2020-2021. emm typing was performed using the CDC protocol and database. Resistance genes were detected by PCR and sequencing, whereas antimicrobial susceptibility testing was performed in clinical and research laboratories with standard techniques. Median patient age was 42 years (23-86 range). 76% (n=50) of isolates were simultaneously resistant to erythromycin and clindamycin, which included both inducible (n=40) and constitutive (n=9) resistance. All emm92 (n=35) and emm11 (n=8) isolates were erythromycin resistant, while the remaining 11% (n=7) of resistant isolates comprised 5 emm types. Susceptible isolates primarily included emm89 (n=6) iGAS. Macrolide resistance was conferred by the plasmid-borne ermT gene in all emm92 isolates and by chromosomally-encoded ermA (n=7), ermB (n=7), and mefA (n=1) in other emm types. Macrolide-resistant iGAS were typically resistant to tetracycline and aminoglycoside antibiotics. Here, we characterized iGAS infections affecting non-pediatric residents across West Virginia. We showed a shift in emm-type distribution compared to historical and national reports, and dominance of macrolide-resistant isolates which raises concern for emerging resistance to commonly-prescribed antibiotics used in treatment of iGAS infections.