Nasopharyngeal carriage, serotype, antimicrobial susceptibility and genotype of pneumococci in young healthy children attending daycare centres in Klang Valley, Malaysia.

Abstract

Background: Streptococcus pneumoniae is a respiratory pathogen that, commonly colonises the nasopharynx in children and the elderly, with 101 serotypes identified. The implementation of pneumococcal conjugate vaccines (PCV) against pneumococcal related diseases has led to a decrease in invasive pneumococcal disease (IPD). In Malaysia, PCV10 was included in national immunisation program in late 2020. Therefore, monitoring serotype distribution and antimicrobial resistance in high-density areas is crucial for vaccine assessment and public health strategies.

Objective: This study aimed to investigate the serotype distribution, antimicrobial resistance patterns, and genetic characteristics of pneumococci in healthy children aged five years and below attending daycare centres in Klang Valley, Malaysia, while indirectly assessing transmission dynamics through nasopharyngeal carriage.

Materials and methods: 168 children across 25 daycare centres provided consent, and their nasopharyngeal swabs collected between January 2023 and May 2024, were analysed for pneumococcal carriage and serotyped by PCR. Antimicrobial susceptibility testing was conducted using the E-test assay. Multilocus sequence typing (MLST) and phylogenetic analysis were performed on isolates with reduced susceptibility.

Results: The pneumococcal carriage rate was 22.6%. Serotype 15C was the most prevalent (15.8%), followed by 23A and 11A (13.2% each). In the E-test assay, 47.4% (18/38) of the isolates were resistant to erythromycin, 28.9% to tetracycline, and 5.3% to penicillin. One isolate was resistant to ceftriaxone, whereas none demonstrated resistance to cefotaxime; decreased susceptibility to the two antibiotics was observed in one isolate, while two others with intermediate susceptibility to either ceftriaxone or cefotaxime alone. Sequence Type (ST) distribution was diverse, with ST338 being the most common (n = 3).

Conclusion: The notable predominance of non-vaccine serotypes (NVTs), particularly 15C and 23A, alongside significant antibiotic resistance, especially to erythromycin and tetracycline, indicates a potential epidemiological shift in the post-PCV era. These results emphasize the need for continuous surveillance to monitor serotype dynamics and antimicrobial resistance patterns in the community.