Changing serotype distribution and resistance patterns among pediatric nasopharyngeal pneumococci collected in Moscow, 2010-2017.

Serotype distribution and antimicrobial resistance were analyzed in 632 nasopharyngeal pneumococcal isolates collected at a single pediatric center in 2010-2017 before and following the introduction of the 13-valent pneumococcal conjugated vaccine (PCV13) in Russia in 2014. The mean prevalence of PCV13 serotypes was 77.7% in 2010-2015 with a significant decline to 58.5% in 2017, which was accompanied by an elevation in serotype 15B/C prevalence (15.1% in 2017), 66% and 26% of 15B/C-pneumococci related to ST1025 and ST1262, respectively. The rate of oxacillin, erythromycin, and clindamycin resistance has increased by 15-20 percentage points from 2010 to 2016, approaching a 40-45% prevalence in 2016. The resistance rates significantly increased over time only in a group of PCV13 serotypes. The growing resistance among serotype 14 pneumococci was associated with expansion of a multidrug-resistant clone of ST143. These results emphasize the need for close monitoring of the constantly changing pneumococcal population.