Epidemiology of invasive pneumococcal disease in older people in Spain (2007-2009): implications for future vaccination strategies

Abstract

Background: Recently, the 13-valent pneumococcal conjugate vaccine (PCV13) has been recommended for adults. We analyzed the epidemiology of invasive pneumococcal disease (IPD) in older adults in Spain before PCV13 introduction.

Methodology/principal findings: IPD episodes, defined as clinical findings together with an invasive pneumococcal isolate, were prospectively collected from patients aged over 65 years in three hospitals in Spain from 2007 to 2009. A total of 335 IPD episodes were collected. Pneumonia was the main clinical syndrome, while chronic obstructive pulmonary disease, diabetes mellitus and cancer were the main underlying diseases. Pneumococcal isolates were serotyped and the molecular typing was performed by PFGE/MLST. PCV13 serotypes accounted for 59.3% of isolates, the most prevalent being serotypes 19A (15.1%), 3 (9.6%), 7F (7.5%), 14 (6.9%) and 1 (5.4%). The most frequent non-PCV13 serotypes were serotypes 16F (4.5%), 22F (3.6%), 24F (3.3%) and 6C (2.1%). The most common genotypes were CC230 (8.5%, serotypes 19A and 24F), CC156 (8.2%, serotypes 9V and 14), ST191 (7.9%, serotype 7F), CC260 (6.6%, serotype 3), ST306 (5.2%, serotype 1), CC30 (4.6%, serotype 16F) and ST433 (3.6%, serotype 22F). Comparing the 335 IPD isolates to 174 invasive pneumococci collected at the same hospitals in 1999-2000, PCV7 serotypes decreased (45.4% vs 18.4%,p<0.001), non-PCV7 serotypes included in PCV13 increased (26.4% vs 41.0%,p = 0.001) and two non-PCV13 serotypes increased (serotype 6C 0% vs 2.1%, p = 0.05; serotype 24F 0.6% vs 3.3%, p = 0.04,).

Conclusion: In our older adult population two serotypes (19A and 3) included in PCV13 accounted for about a quarter of IPD episodes in people ≥65 years. Non-PCV13 emerging serotypes should be carefully monitored in future surveillance studies.

Figure 1. Serotype distribution of invasive pneumococci collected from adults over 65 by period.

The serotype distribution in the two periods analyzed 1999–2000 (pre-PCV7, n = 174 isolates) and 2007–2009 (pre-PCV13, n = 332 isolates) is showed. Statistically significant changes are indicated with an asterisk. Overall, PCV7 serotypes decreased from 45.4% (1999–2000) to 18.4% (2007–2009, p<0.001). Non-PCV7 serotypes included in PCV13 increased from 26.4% to 41.0% (p = 0.001). Serotype 6A is not included in PPV23. In 2007–2009 period, the proportion of IPD isolates included in PCV7 was 18.4%, with the proportions being 59.3% in PCV13 and 73.8% in PP23V.

Figure 2. Population structure of invasive S. pneumoniae collected from older people in Spain.

The overall eBURST analysis of MLST data for 463 invasive pneumococci showed 22 clonal groups and 46 singletons (blue lines: single locus variant; and pink lines: double locus variant). The most frequent genotypes were: CC156 (11.2%), CC260 (8.2%), ST191 (6.0%), CC230 (5.8%), ST247 (4.3%), CC53/62 (4.1%), CC30 (3.7%), ST306 (3.7%), CC180 (3.5%) and ST433 (3.2%).