Two-year surveillance of emm types and antibiotic resistance of pediatric group A streptococcal pharyngitis strains in the central part of Italy

Introduction. Pharyngitis caused by group A Streptococcus (GAS) is a common infection and, though self-limiting, may be associated with suppurative or non-suppurative sequelae. An insight on the dissemination of clones with specific emm types provides a significant epidemiological picture of the population structure and dynamics of GAS isolates circulating in Italy. Additionally, knowing the antimicrobial resistance rate of the group A Streptococci population gives important information for the medical treatment of streptococcal infections. The aim of this study was to isolate GAS during the 2012 and 2013 epidemic waves of pharyngitis and characterize their emm types distribution and frequencies, and antibiotic profile. Methods. 605 GAS isolates were collected in the central part of Italy during winter-spring 2012 and 2013 from pharyngotonsillitis. We determined their emm type according to CDC guidelines. Benzylpenicillin, erythromycin, clindamycin, tetracycline, linezolid, rifampicin, quinupristin/dalfopristin, and norfloxacin susceptibilities were tested by disc diffusion following the EUCAST guidelines. Results. Thirteen emm types represented 90% of the isolates, seven of which accounted for almost 70% of the strains (emm1, 4, 12, 89, 6, 3, 5). The overall distribution of emm types between 2012 and 2013 was significantly different (P < 0.001) with major contributions given by emm types 1, 3, and 89 (P ≤ 0.05). All the isolates were susceptible to each antibiotic tested except to clindamycin ( ̴4%), tetracycline ( ̴5%), erythromycin ( ̴7%), and norfloxacin ( ̴6%). Discussion and Conclusions. In view of the overall emm distribution and the high degree of diversification among the strains, the 26-valent vaccine under clinical evaluation would have covered 75% of the emm types, while the 30-valent form would have approached 98% of coverage.