Pneumococcal genotype 23B1 as a driver of increased 23B serotype carriage, penicillin non-susceptibility, and invasive disease in Belgium: a retrospective analysis

Subtitle:a retrospective analysis

Abstract:Streptococcus pneumoniae serotype 23B, a non-vaccine serotype, has shown an increasing prevalence and penicillin non-susceptibility among carriage and invasive pneumococcal disease (IPD) isolates. Recently, a novel penicillin non-susceptible genotype has emerged, named 23B1. In the framework of the Belgian pneumococcal carriage study, we studied the prevalence of 23B(0)/23B1 among 586 23B strains (2016-2022) in 172 day care centers from 6- to 30-month-old children and among 130 pediatric 23B IPD isolates (2007-2021). Pneumococci were whole genome sequenced to determine the capsular polysaccharide genotype and sequence type (ST). Antimicrobial susceptibility testing determined penicillin and amoxicillin MICs, as well as resistance to co-trimoxazole and levofloxacin. 23B carriage was stable during 2016 - 2022 except in the 2020-2021 winter season when it increased. The proportion of genotype 23B1 compared to 23B(0) decreased from 2016 - to 2022 but remained consistently higher than 23B(0). In 2020-2021, an increase in the proportion of 23B1 was reflected in an overall increase in 23B carriage. All increases in 23B IPD cases were almost entirely driven by 23B1. The median penicillin MICs were significantly different for 23B(0) (0.03 mg/L) and 23B1 (0.25 mg/L). In 2021, increased intermediate levofloxacin susceptibility was noted in 23B. 23B1-associated ST2372 was the most prevalent ST in carriage and IPD during 2013-2022. We show that an increase in 23B carriage among children was paralleled in pediatric IPD in Belgium, reiterating the utility of pneumococcal surveillance in the day care population. Serotype 23B is reported worldwide as an important pediatric non-PCV13 serotype with reduced penicillin susceptibility, with 23B1 as the presumed driver for the increased prevalence.

Publication year:2025

Keywords:Biology, Microbiology

Accessibility:Open