Risk factors for community-acquired pneumonia in older adults after the introduction of childhood 13-valent pneumococcal conjugate vaccine: A multi-center case-control study in Japan

<bold>Introduction:</bold> Community-acquired pneumonia (CAP) is a leading cause of morbidity and mortality worldwide and underscoring the necessity of identifying its risk factors to implement preventative measures. Recent studies have suggested a change in the epidemiological landscape of CAP in older adults, with serotype replacement and herd immunity after the introduction of the 13-valent pneumococcal conjugate vaccine (PCV13) in children. However, few studies assessed the contemporary risk factors for CAP. <bold>Objective:</bold> To clarify the risk factors for CAP in the older adults in Japan after the introduction of childhood PCV13. <bold>Methods:</bold> This multi-center, matched case-control study across 41 hospitals and clinics included patients aged 65 years or older diagnosed with CAP between October 2016 and September 2019, after childhood PCV13 was introduced. Each case was matched with up to five non-pneumonia controls based on sex, school year, date of visit, and medical institution. We used conditional logistic models to calculate the adjusted odds ratio (aOR) and 95% confidence interval (CI) of each risk factor. <bold>Results:</bold> A total of 738 participants (143 cases and 595 controls) were analyzed using multivariate analysis. Low BMI (<18.5), living with children, and inability to independently perform activities of daily living (ADL) were associated with significant aOR values of 1.78 (95% CI: 1.02-3.11), 5.92 (95% CI: 2.72-12.91), and 2.48 (95% CI: 1.14-5.36), respectively. <bold>Conclusions:</bold> This study suggests low BMI, living with children, and increased dependence in ADL are independent risk factors for CAP in older adults.