Changes in the Pneumococcal Vaccine Serotypes in Adult Noninvasive Pneumonia after the Introduction of Pneumococcal Conjugate Vaccination for Children

CONTEXT: Although the incidence of invasive pneumococcal infections in children has decreased since the introduction of pneumococcal conjugate vaccines (PCVs), the appearance of serotype replacements has continued to increase. AIMS: We examined the frequency of serotype replacements in adult cases of pneumococcal pneumonia. Furthermore, the transition in the coverage of vaccine serotypes (VTs) to non-VTs (NVTs) was also examined. SETTINGS AND DESIGN: We investigated all confirmed cases of pneumococcal pneumonia in 303 adult patients admitted to Yamagata Saisei Hospital between April 2006 and March 2015. MATERIALS AND METHODS: Pneumococcal serotypes were determined by testing for a specific type of antiserum using the capsular swelling method. STATISTICAL ANALYSIS USED: Chi-square tests were used to compare patient characteristics. RESULTS: Annually, the number of admitted patients ranged from 24 to 43, with most of them being men (64.7% of the total patient cohort). Although many cases involved some underlying conditions, the rate of pneumococcal vaccination remained low. The average rate of multigeneration housing was high (37.6%). The rates of pneumococcal vaccine coverage declined since 2013 (7-valent PCV (PCV7), 18.5%; PCV13, 59.3%; and 23-pneumococcal polysaccharide vaccine (PPSV23), 66.7%) and were <50% for each vaccine (PCV7, 4.7%; PCV13, 32.6%; and PPSV23, 48.8%) in 2015. In addition, the VTs were replaced with NVTs in 2015 (48.8% vs. 51.2%). CONCLUSIONS: The frequency of NVTs in adult pneumococcal pneumonia increased in 2013, with the frequency exceeding that of the vaccine forms in 2015. Regular PCV vaccination of children and multigeneration housing seem to be associated with this reversed trend.