Emergence of macrolide-resistant Streptococcus pyogenes emm12 in southern Taiwan from 2000 to 2019.

Background: Group A Streptococcus (GAS) is an important pathogen causing morbidity and mortality worldwide. Surveillance of resistance and emm type has important implication to provide helpful information on the changing GAS epidemiology and empirical treatment.

Methods: To study the emergence of resistant GAS in children with upper respiratory tract infection (URTI), a retrospective study was conducted from 2000 to 2019 in southern Taiwan. Microbiological studies, including antibiotic susceptibility, were performed. GAS emm types and sequences were determined by molecular methods. The population was divided into two separate decades to analyze potential changes over time. The 1st decade was 2000-2009; the 2nd decade was 2010-2019. Multivariate analyses were performed to identify independent risk factors associated with macrolide resistance between these periods.

Results: A total of 320 GAS from 339 children were enrolled. Most of the children (75%) were under 9 years of age. The most common diagnosis was scarlet fever (225, 66.4%), and the frequency increased from 54.8% in the 1st to 77.9% in the 2nd decade (p < 0.0001). There was a significant increase in resistance to erythromycin and azithromycin from 18.1%, 19.3% in the 1st to 58.4%, 61.0% in the 2nd decade (p < 0.0001). This was associated with clonal expansion of the GAS emm12-ST36 which carrying erm(B) and tet(M) from 3.0% in the 1st to 53.2% in the 2nd decade (p < 0.0001).

Conclusions: Significant emergence of macrolide-resistant GAS emm12-ST36 in children supports the need for continuing surveillance and investigation for the clonal virulence.