Prevalence, Serotype Distribution, and Risk Factors Associated With Streptococcus pneumoniae Carriage in Older Adults in Denmark, 2019-2022

Why clinicians should know about it

• Picked for Immunology and Allergy (paper of the day, 6 August 2026).

Abstract

BACKGROUND: The burden of pneumococcal disease in older adults remains high in the postpneumococcal conjugate vaccine (PCV) era. We hypothesized that older adults may represent a carriage reservoir of Streptococcus pneumoniae. METHODS: Paired naso- and oropharyngeal (NP and OP) swabs and questionnaires were collected during 2019-2022 from adults ≥65 years of age. Pneumococcal carriage and serotype distribution were determined by phenotypical and molecular methods. RESULTS: A total of 172/1764 participants (9.8% [95% confidence interval {CI} 8.4-11.2]) were positive for carriage of S. pneumoniae by either culture (0.3%) or lytA/piaB DNA in NP (2.0%) or OP (8.4%) samples. Overall, 118 serogroup- or serotype-specific carriage events were identified by multiplex polymerase chain reaction across 16 distinct serospecificities in 93 samples, while 79 samples were nontypeable. PCV13 types accounted for 8.0%, nonvaccine types for 11.0% and polysaccharide pneumococcal vaccine 23 (PPV23)/non-PCV13 types for 81.0%. All carriage serotypes, except serotype 2, had been identified in invasive pneumococcal disease (IPD) isolates among adults ≥65 years during 2019-2022. Having young grandchildren was associated with increased odds of carriage (adjusted odds ratio [OR] 1.8, 95% CI 1.2-2.5, P = .0031). No association between PPV23 immunization and carriage was observed (OR 0.8, 95% CI .5-1.3). CONCLUSIONS: Older adults were carriers of a wide range of IPD-causing serotypes. Both carriage and IPD serotypes were mainly comprised of non-PCV13 serotypes. Immunization with higher valency conjugated vaccines is likely required to reduce residual pneumococcal disease among older adults.

Abstract as published, via PubMed.