Clinical features of adults with seven-valent-conjugated-vaccine-serotype pneumococcal pneumonia

Background: Despite the reduction in adult invasive pneumococcal disease through 'herd protection' consequent to the introduction of childhood pneumococcal conjugate vaccination (PCV), a significant proportion of adults continue to develop pneumococcal pneumonia caused by one of the seven serotypes included in the seven-valent conjugated pneumococcal vaccine (PCV7). The clinical features and outcomes of these adults have not been previously reported. Methods: Adults recruited over a three year period to a large prospective cohort study of community acquired pneumonia (CAP) were investigated for pneumococcal serotypes using a validated multiplex immunoassay (Bio-plex). The baseline characteristics and outcomes of adults with PCV7-serotype CAP in comparison to those with non-PCV7-serotype CAP were established. Results: Pneumococcal aetiology was identified in 415 of 1166 (35.6%) individuals, and a serotype determined in 287(69.2%). Following exclusion of three individuals with both a PCV7 and non-PCV7 serotype, 77 of the remaining 284(27.1%) adults had CAP due to PCV7 serotypes. Adults with PCV7-serotype CAP were older (median years (inter-quartile range) 73.3 (60.8-84.4) versus 65.0 (46.1-78.0); p = 0.001) and were more likely to have a World Health Organisation performance status >= 1 (odds ratio (OR) 2.05, 95% confidence interval (CI) 1.21-3.50). The presence of stroke (adjusted OR 2.84, 95% CI 1.36-5.95) and dementia (adjusted OR 3.55, 95% CI 1.26-9.94) as underlying co-morbid illnesses were independently associated with PCV7-serotype CAP; 30-day mortality was significantly greater in adults with PCV7-serotype CAP (adjusted OR 4.38,95% CI 1.85-10.34). Conclusion: A significant proportion of adults continue to develop PCV7-serotype CAP in the era of childhood pneumococcal conjugate vaccination. These adults are more likely to have stroke and dementia as underlying co-morbid illnesses, and have a higher 30-day mortality. A combination of pneumococcal transmission factors, host factors and pneumococcal serotype specific characteristics are likely to explain these findings. (C) 2014 Elsevier Ltd. All rights reserved.