Pneumococcal bacteraemia in adults over a 10-year period (2011-2020): a clinical and serotype analysis.

Background: Streptococcus pneumoniae (pneumococcus) is a human nasopharyngeal tract coloniser responsible for invasive pneumococcal disease, which is largely vaccine preventable. Vaccination is recommended from birth for all, and through adulthood for those with risk conditions.

Aims: To describe the clinical and serotype analysis of pneumococcus bacteraemia over a 10-year period.

Methods: A 10-year (February 2011-December 2020) retrospective review was performed on all adult (age ≥18 years) pneumococcus bacteraemia presenting to the four public hospitals in Western Sydney, Australia. Comorbidities and risk factors were recorded.

Results: Three hundred unique episodes of S. pneumoniae bloodstream infection (SPBI) were identified during the study period. The median age for SPBI was 63 years with 31.7% aged 70 years or older. A 94.7% had one or more risks factors for SPBI. Pneumonia was reported in 80% of all SPBI, whereas meningitis was reported in 6% and infective endocarditis in <1%. Asplenia was noted in 2.4%. Seven- and 30-day mortality was 6.6% and 11.9%, with a higher 30-day mortality in those aged ≥70 years (24.4%). The serotype distribution showed 7-valent conjugate vaccine covered 11.0% of all isolates, whereas 13-valent conjugate vaccine (13vPCV) and a 23-valent polysaccharide vaccine (23vPPV) covered 41.7% and 69.0% respectively. Immunisation details were available for 110 individuals, of whom, only 7.3% had received pneumococcal vaccination.

Conclusions: Most patients with pneumococcal bacteraemia had age- or comorbidity-related risk factors but were not vaccinated. Two-thirds of cases occurred in people aged <70 years. 13vPCV and 23vPPV covered 41.7% and 69.0% of bacteraemic isolates.