Risk factors for community-acquired pneumonia in older adults in Japan after the introduction of the childhood PCV13

BACKGROUND: Community-acquired pneumonia (CAP) remains a leading cause of death globally. Although childhood 13-valent pneumococcal conjugate vaccine (PCV13) has altered the epidemiology of pneumococcal disease in children, risk factors for CAP in older adults remain insufficiently explored. Additionally, few studies have compared risks between those aged 65-74 and ≥ 75 years. We evaluated risk factors for CAP in older Japanese adults by age. METHODS: We conducted a secondary analysis of data from a multicenter, nationwide case-control study conducted between October 2016 and December 2019. Cases were individuals aged ≥ 65 years with CAP. Up to five controls per case were matched by sex, fiscal-year age, and visit date. Clinical and lifestyle data were questionnaire-based. Adjusted odds ratios (aORs) were calculated for participants overall and stratified by age (65-74 and ≥ 75 years) using conditional logistic regression. RESULTS: Analysis included 142 cases and 596 controls. CAP risk was associated with living with children ≤ 6 years (aOR: 6.15, 95% confidence interval [CI]: 2.84-13.32), low body mass index (BMI) (< 18.5 kg/m²) (aOR: 1.78, 95% CI: 1.02-3.09), and impaired activities of daily living (ADL) (aOR: 2.44, 95% CI: 1.12-5.30). High BMI (≥ 25.0 kg/m²) was associated with a reduced risk (aOR: 0.55, 95% CI: 0.31-0.95). Among those aged 65-74 years, living with children ≤ 6 years (aOR: 4.89, 95% CI: 1.83-13.08) was a risk factor for CAP, whereas high BMI (aOR: 0.41, 95% CI: 0.18-0.89) and gastrointestinal disease (aOR: 0.19, 95% CI: 0.04-0.84) were associated with a reduced risk. Among those aged ≥ 75 years, chronic obstructive pulmonary disease (aOR: 3.59, 95% CI: 1.29-9.93), asthma (aOR: 2.99, 95% CI: 1.25-7.16), living with children ≤ 6 years (aOR: 11.62, 95% CI: 3.12-43.33), and impaired ADL (aOR: 2.90, 95% CI: 1.10-7.65) were risk factors for CAP. Only living with children ≤ 6 years was significant for pneumococcal CAP (aOR: 7.22, 95% CI: 1.23-42.34). CONCLUSIONS: Living with children ≤ 6 years remains a major CAP risk factor in older adults after childhood PCV13 introduction. However, risk factors differ by age. Respiratory comorbidities and functional decline are dominant drivers of CAP in adults aged ≥ 75 years. Prevention strategies should consider age-specific dominant risk factors.