Trend change of nasopharyngeal colonization with Streptococcus pneumoniae and non-typeable Haemophilus influenzae in children attending daycare centres: nationwide population-based study, South Korea 2014 and 2019

Background: Nasopharyngeal (NP) colonization with Streptococcus pneumoniae and non-typeable Haemophilus influenzae (NTHi) is common in children, and may evolve as the source of invasive infec-tions. In Korea, the pneumococcal conjugate vaccines (PCVs) were introduced > 10 years ago, enabling the authors to study the effect of the vaccine in preventing carriage. Methods: NP swabs were taken and a household survey was conducted at daycare centres located in different regions of Korea in 2014 and 2019. Pneumococcal serotypes were identified using the Quellung method and sequencing. NTHi were identified based on pilA and bexA genes. Results: In total, 1460 NP swabs were obtained with pneumococcal carriage rates of 36.4-42.1% and NTHi carriage rates of 36.5-26.7%. Among children carrying pneumococci, a significant increase was seen in serotype 23A between 2014 and 2019 (from 12.6% to 22.0%; P = 0.005). Children who had received PCV were at lower risk of vaccine-type carriage (2.9% vs 0.8%; P = 0.005). Conclusions: Between 2014 and 2019, the proportion of children carrying serotype 23A increased sig-nificantly, while the carriage rate of NTHi decreased. Continuous surveillance is needed to assess the long-term effects of the PCVs on carriage dynamics of pneumococcus and NTHi. (c) 2021 The Author(s). Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Automated summary

The study in Korea between 2014 and 2019 found that the carriage rates of Streptococcus pneumoniae and non-typeable Haemophilus influenzae in children varied, with a significant increase in carriage of serotype 23A of S. pneumoniae. Children who had received pneumococcal conjugate vaccines had a lower risk of vaccine-type carriage. Continuous surveillance is necessary to evaluate the long-term effects of PCVs on the carriage dynamics of these bacteria.