Changes in epidemiologic characteristics and antimicrobial resistance of isolated over 10 years from Japanese children with pharyngotonsillitis.

Pharyngotonsillitis caused by (group A streptococci, or GAS) is among the most common infections treated with antibiotics in pediatric patients. This study aimed to analyse changes in molecular epidemiology and antibiotic susceptibility among GAS isolates in three study periods spanning 10 years.. GAS isolated from paediatric patients with pharyngotonsillitis during Period I (mid-2007 to 2008, =235), Period II (2012, =210), and Period III (2018, =189) were analysed for type, multilocus sequence type (MLST), antibiotic susceptibility, and macrolide (ML)- and quinolone (QL)-resistance genes. Over 20 % of isolates represented 1 and 12 types, remaining common in all three periods. Among other types, 4 was common in Period I, 28 and 89 in Period II, and 3 and 89 in Period III. All isolates remained highly susceptible to penicillins and cephalosporins. Isolates possessing or genes mediating ML resistance increased from 34.9 % in Period I to 60.9 % in Period II, but fell to 27.5 % in Period III. QL-resistant isolates with amino acid substitutions affecting ParC and/or GyrA gradually increased from 11.5 to 14.3 %. Specific sequence types identified by MLST and typing were associated closely with ML or QL resistance. Our findings indicate that even in ambulatory care, antibiotic choice for these infections should be based on rapid identification and characterization of causative pathogens.