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Background: Expansion of the single sequence type 3 (ST3) was associated with a high macrolide resistance rate among Mycoplasma pneumoniae in Korea during the 2014–2016 epidemic. This study investigates the macrolide resistance rate and genetic diversity of the subsequent epidemic of M. pneumoniae pneumonia in 2019–2020. Methods: The culture for M. pneumoniae was developed from 1228 respiratory samples collected from children with pneumonia in four hospitals in Korea between January 2019 and January 2020. Determination of macrolide resistance and multilocus sequence typing analysis were performed on M. pneumoniae isolates. eBURST analysis was applied to estimate the relationships among strains and to assign strains to a clonal complex. Results: M. pneumoniae was cultured in 93 (7.6%) of 1228 clinical samples. The overall macrolide resistance rate of M. pneumoniae strains was 78.5% (73/93). Of the nine STs identified, three were novel. The most common ST was ST3 (66 [71.0%]) followed by ST14 (18 [19.4%]) and ST7/ST15 (2 [2.2%] each). Three STs (ST3, ST14, and ST17) exhibited macrolide resistance. The macrolide resistance rates of ST3 and ST14 were 98.5% (65 of 66) and 38.9% (7 of 18), respectively. Conclusion: Compared to the previous outbreak in 2014–2016, the overall macrolide resistance remained high; however, an increasing proportion of macrolide resistance was observed within ST14 strains in 2019–2020.

ABSTRACT: 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 infections. 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 significantly, 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.

Objectives: In Korea, the National Immunization Program provided trivalent inactivated influenza vaccines (IIV3) to all children aged 6–59 months during the 2017–2018 season. In this study, we aimed to evaluate the vaccine effectiveness (VE) of IIV3 in children during the 2017–2018 season. Methods: Children aged 6–59 months who were tested for influenza for their acute respiratory illness in four hospitals during the 2017–2018 influenza season were included. We estimated the VE of IIV3 by test-negative case-control design based on the rapid influenza diagnostic test (RIDT) or reverse transcription polymerase chain reaction (RT-PCR) test results. Results: A total of 4738 children were included in this study. The number of laboratory-confirmed influenza cases was 845 (17.8%), and there were 478 cases of influenza A and 362 cases of influenza B. The adjusted VE based on RT-PCR was 53.4% (95% CI, 25.3–70.5) against any influenza, 68.8% (95% CI, 38.7–84.1) against influenza A, and 29.7% (95% CI, −35.1 to 61.8) for influenza B. The adjusted VE based on RIDT was 14.8% (95% CI, −4.4 to 30.0) against any influenza, 24.2% (95% CI, 3.1–40.2) against influenza A, and −5.1% (95% CI, −42.6 to 21.4) against influenza B. Age-specific VE based on RT-PCR against any influenza was 44.1% (95% CI, −0.2 to 67.8) in children aged 6 months to 2 years and 59.3% (95% CI, 8.8–81.9) in children aged 3–