Trends of serotypes and resistance among Streptococcus pneumoniae in the UK and Ireland (1999–2019)

Objectives:
This study aimed to report the serotype distribution of Streptococcus pneumoniae isolates from UK and Irish patients with bacteraemia or community-associated lower respiratory tract infections (CA-LRTI). Depending upon the year, these were from 23 to 39 sentinel laboratories and were collected between 1999 and 2019, thus spanning the introduction of pneumococcal conjugate vaccines, PCV7 and PCV13.

Methods:
Pneumococcal identification, susceptibility testing and serotyping were undertaken by a central laboratory. Changes in serotype distributions and among the predominant types showing antibiotic non-susceptibility were reviewed in relation to vaccine deployment.

Results:
Following the introduction of PCV7 (2006) and PCV13 (2010), major shifts occurred in serotype prevalence for both bacteraemia and CA-LRTI. PCV7 types and most PCV13 types (but not 3 and 19A) were largely or wholly displaced. Many of the displaced types (e.g. 6B, 9V, 14, 19F and 23B) had been internationally prevalent and were associated with antibiotic resistance. Other serotypes—many included within the older pneumococcal polysaccharide vaccine, PPV23—expanded into the space, with serotype 8 becoming especially prominent in bacteraemia, though not respiratory infections. Further increasingly prevalent types included 9N, 10A, 12F and 22F. Serotype 15A, often multi-resistant, rose then fell in relative importance after deployment of PCV13. Among the currently most prevalent types, serotype 3 is rarely resistant to agents besides tetracyclines and bloodstream serotype 8 isolates mostly are fully susceptible.

Conclusions:
These data offer a comparison of serotypes associated with bacteraemia and respiratory disease over two decades in the UK and Ireland.