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Invasive pneumococcal disease in persons with predisposing factors is dominated by non-vaccine serotypes in Southwest
Karin Bergman1,2, Tor Härnqvist3,4, Erik Backhaus5
1Department of Infectious Diseases, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. karin.bergman@gu.se.
Insights
Pneumococcal conjugate vaccine (PCV) introduction led to decreased PCV13 serotypes, but non-PCV13 serotypes increased, particularly in older adults and those with predisposing conditions. Serotype 3 remained prevalent and caused severe disease.
Area of Science:
- Infectious Diseases
- Vaccinology
- Epidemiology
Background:
- The introduction of pneumococcal conjugate vaccines (PCV7, PCV13, PCV10) in Sweden aimed to reduce invasive pneumococcal disease (IPD).
- Understanding serotype distribution shifts post-vaccination is crucial for public health strategies.
Purpose of the Study:
- To analyze pneumococcal serotype distribution in relation to predisposing factors, clinical manifestations, and outcomes following PCV introduction.
- To assess the impact of PCV7, PCV13, and PCV10 on IPD epidemiology over seven years.
Main Methods:
- Retrospective cohort study of 1278 patients with 1304 IPD episodes (2009-2015) in Region Västra Götaland, Sweden.
- Serotyping of pneumococcal isolates and statistical analysis of associations between serotypes and clinical characteristics.
- Time-trend analysis of IPD episodes caused by specific serotypes.
Main Results:
- Prevalence of PCV13 serotypes decreased significantly (76% to 25%), while non-PCV13 serotypes increased, especially in patients ≥65 years and those with comorbidities.
- Patients with predisposing factors (malignancy, immune deficiency, renal disease) were more likely to have IPD caused by non-PCV13 serotypes.
- Serotype 3 (PCV13) was associated with severe disease and ICU admissions; serotypes 1 and 7F caused IPD in younger, healthier individuals.
Conclusions:
- Non-PCV13 serotypes are now the primary cause of IPD in Southwest Sweden, particularly in vulnerable populations.
- Serotype 3 remains a significant public health concern within the PCV13 vaccine, often leading to severe IPD.
- Vaccination strategies may need to adapt to address the increasing prevalence of non-vaccine serotypes.
Background:
The pneumococcal conjugate vaccine PCV7 was introduced in Southwest Sweden in the child vaccination program in 2009, followed by PCV13 in 2010 and PCV10 in 2015. In this retrospective cohort study we assessed the pneumococcal serotype distribution in relation to predisposing factors, clinical manifestations and outcome during seven years after PCV introduction.
Methods:
Clinical data from 1278 patients with 1304 episodes of invasive pneumococcal disease (IPD) between January 2009 and December 2015 in Region Västra Götaland, Sweden, were retrospectively collected from medical records. Pneumococcal isolates were serotyped by gel diffusion and/or Quellung reactions performed at the Public Health Agency in Sweden. Associations between serotypes and clinical characteristics were statistically evaluated by use of Fisher's exact test, Mann-Whitney U test and Logistic regression analysis, whereas IPD episodes caused by serotypes over time were analyzed by Mantel-Haenszel chi-square test.
Results:
With the exception of serotype 3, the prevalence of PCV13 serotypes decreased during the study period, from 76% (n = 157) of all IPD episodes in 2009 to 25% (n = 42) in 2015 (p < 0.001) while non-PCV13 serotypes increased, mainly among patients ≥65 years and in patients with predisposing factors, including cardiovascular disease, pulmonary disease and malignancy (p < 0.001 for all). Patients with predisposing factors, including those with malignancy, immune deficiency or renal disease, were more likely to have IPD caused by a serotype not included in PCV13 rather than a vaccine-included serotype. Serotype 3 was associated with intensive care unit admissions while serotype 1 and 7F caused IPD among healthier and younger patients. PCV13 serotypes were associated with invasive pneumonia, and non-PCV13 serotypes were associated with bacteremia with unknown focus and with manifestations other than pneumonia or meningitis.
Conclusions:
Non-PCV13 serotypes caused the majority of IPD cases in Southwest Sweden, especially in patients ≥65 years and in patients with predisposing factors. Serotype 3, included in PCV13, was prevalent and often caused severe disease.
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