Effects of 7-valent pneumococcal conjugate 1 vaccine on the severity of adult 2 bacteremic pneumococcal pneumonia

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PurposeThe introduction of a 7-valent conjugate pneumococcal vaccine (PCV7) in children largely affected the prevalence of adult pneumococcal pneumonia. In this study we investigated whether the clinical severity of adult bacteremic pneumococcal pneumonia has also altered following the introduction of pediatric PCV7 vaccination. MethodsAdults hospitalized with bacteremic pneumococcal pneumonia between 2001 and June 2011 at two Dutch hospitals were included retrospectively. Clinical data on patient characteristics, comorbidities and severity of disease were obtained and pneumococcal serotypes were determined. ResultsAmong 343 patients investigated, those infected with PCV7 serotypes had a higher PSI score (p=0.0072) and mortality rate (p=0.0083) compared with the remainder of the cohort. Since the introduction of PCV7 the proportion of pneumococcal pneumonias caused by serotypes 1 and 7F (p-values 0.037 and 0.025) increased, as well as the rate of pleural effusion and empyema (p-values 0.011 and 0.049). Whilst de proportion of adults infected with PCV7 serotypes decreased after the introduction of PCV7 (p=0.015), PSI scores in these patients remained higher (p=0.030), although mortality rates between PCV7 and non PCV7 types equalized. After the introduction of PCV7 a marked shortening in hospital stay was observed only among patients infected with non PCV7 serotypes (p=0.019). ConclusionsThe introduction of pediatric PCV7 vaccination was accompanied by subtle changes in clinical severity of adult bacteremic pneumococcal pneumonia. Expansion of serotypes covered by pneumococcal vaccination may again influence the clinical presentation of disease.