# Serotype diversity and risk factors for pneumococcal carriage among healthy children in Klang Valley, Malaysia: A pre-vaccination cross-sectional study

## TL;DR

This study examines pneumococcal carriage in unvaccinated children in Malaysia, finding that over a third carry the bacteria, with household size and non-vaccine serotypes playing significant roles.

## Contribution

Provides pre-vaccination baseline data on pneumococcal carriage and serotype diversity in Klang Valley, Malaysia.

## Key findings

- 39.6% of children carried pneumococcus before PCV vaccination.
- 67.5% of carriers had multiple serotypes, and household size >5 increased carriage risk.
- Non-vaccine serotypes were more prevalent than vaccine serotypes in unvaccinated children.

## Abstract

•Overall, 39.6% of children had pneumococcal carriage pre-pneumococcal conjugate vaccine (PCV) vaccination.•Household size of more than five significantly influenced pneumococcal carriage.•A total of 67.5% of children carry multiple serotype pre-PCV vaccination.•Non-vaccine serotypes predominantly colonize unvaccinated children in Klang Valley.

Overall, 39.6% of children had pneumococcal carriage pre-pneumococcal conjugate vaccine (PCV) vaccination.

Household size of more than five significantly influenced pneumococcal carriage.

A total of 67.5% of children carry multiple serotype pre-PCV vaccination.

Non-vaccine serotypes predominantly colonize unvaccinated children in Klang Valley.

Carriage of Streptococcus pneumoniae among children aged <5 years facilitates transmission and invasive pneumococcal disease (IPD) progression, contributing to global childhood morbidity and mortality. Pneumococcal conjugate vaccines (PCVs) can reduce disease and carriage prevalence, though their effectiveness varies by regional serotype distribution. Malaysia introduced PCVs into the National Immunization Program in late 2020, but data on pneumococcal carriage and risk factors in children before vaccine implementation remain limited. This study aims to identify pneumococcal carriage, diversity, and risk factors among the unvaccinated children in Klang Valley, Malaysia.

A cross-sectional study conducted from August 2018 to May 2019 involved 101 healthy children aged 2-5 years from 30 childcare centers in Klang Valley, Malaysia. Oropharyngeal swabs, which are more acceptable for young children although less sensitive than nasopharyngeal swabs for pneumococcal detection, were collected and enriched in Todd Hewitt Broth before DNA extraction. Carriage was identified using real-time polymerase chain reaction (PCR) targeting lytA gene, with positive samples serotyped using conventional multiplex PCR. Demographic and environmental data from structured questionnaires were analyzed for associations with pneumococcal carriage and multiple serotype colonization using logistic regression, chi-square, and Fisher exact test.

Pneumococcal carriage was detected in 39.6% (n = 40) of children, with 33 distinct serotypes identified. Both vaccine serotypes (VTs) and non-VTs were detected, with 67.5% of carriers colonized by multiple serotypes. Household size >5 members was significantly associated with carriage (adjusted odds ratio 4.62, 95% confidence interval 1.07-23.10, P = 0.047), while no demographic, behavioral, or environmental factors were significantly associated with multiple serotype colonization. VTs detected (19F, 6A/6B, 3, 1, and 5) were previously associated with IPD in Malaysia.

This study provides crucial pre-PCV baseline data on pneumococcal carriage, serotype diversity, and risk factors in children of Klang Valley, Malaysia. The high prevalence of NVTs and frequent co-colonization highlight the need for ongoing surveillance to detect serotype replacement and guide evaluation of higher-valency PCVs. These findings can inform national immunization policy and strengthen strategies for monitoring vaccine impact in Malaysia.