Prevalence and long-term persistence of beta-haemolytic streptococci throat carriage among children and young adults.

Introduction. Among beta-haemolytic streptococci, Streptococcus pyogenes (GAS) is the prototype agent of bacterial pharyngitis and causes other human infections. Streptococcus dysgalactiae subsp. equisimilis (SDSE) causes GAS-like infections, while Streptococcus agalactiae (GBS) is a common neonate pathogen that is rarely associated with pharyngitis.Aim. To determine the prevalence and persistence of beta-haemolytic streptococci throat carriage and type the bacterial population.Methods. Throat swabs were collected from 121 children and 127 young adult volunteers and cultured. Colonized volunteers were screened quarterly, for up to 1 year, while beta-haemolytic streptococci could be detected. Isolates were identified and submitted to antimicrobial susceptibility testing and epidemiological typing.Results. Carriage was detected in 34 (13.7 %) volunteers. Seventeen children carried GAS (14 %), while 17 young adults carried SDSE (8, 6.3 %), GBS (4, 3.1 %), GAS (3, 2.4 %) and the Streptococcus anginosus group (2, 1.6 %). Persistent carriage was detected for up to 6 months in two children and for up to 1 year in three young adults. Three new emm subtypes were found, emm87.16 and emm90.9 (GAS) and stC36.11 (SDSE). While the GAS population among children was unexpectedly clonal, substantial genetic diversity was found among the isolates recovered from young adults. Resistance to erythromycin, clindamycin and tetracycline was detected in GAS, GBS and SDSE recovered from young adults.Conclusions. Prevalence was slightly greater among children, but persistent carriage was greater among young adults, with SDSE being the species most associated with persistence. Few sources seemed to disseminate GAS among children, since only two clonal types were found. The volunteers hosted pathogenic streptococci persistently, including macrolide-resistant strains.