Outcomes and patient characteristics among patients with infective endocarditis according to age groups: a nationwide cohort study

Background Infective endocarditis (IE) remains associated with substantial morbidity and mortality despite advances in diagnostics and treatment. IE predominantly affects elderly patients with multiple comorbidities or prosthetic valves, but also occurs in younger individuals, often in association with congenital heart disease or intravenous drug use. Understanding age-related differences in IE is essential for optimizing diagnostic strategies, risk stratification, and treatment decisions across the heterogeneous IE population. Purpose To characterize age-related differences in IE by examining microbiological aetiologies, comorbidity profiles, frailty, surgical management, and mortality across age groups. Methods Using Danish nationwide registries, we identified patients with first-time IE between 2010–2023 and categorized them into three age groups. Cumulative one-year mortality was assessed using the Kaplan-Meier estimator. Cumulative 182-day incidence of relapse bacteraemia after discharge was computed using the Aalen-Johansen estimator. Adjusted hazard ratio analyses were performed using multivariable Cox regression. Results A total of 7,473 patients were included and stratified by age: <65 years (N = 2,094, 71.8% male); 65–74 years (N = 2,028, 73.9% male), and ≥75 years (N = 3,351, 63.4% male). The prevalence of cardiovascular comorbidities and cardiac devices increased with age, as did the mean Hospital Frailty Risk Score. Enterococcus-IE was more prevalent among older patients (<65 years: 7.7%, 65-74 years: 16.1%, ≥75 years: 21.4%), whereas S. aureus-IE (34.4%, 29.4%, 29.0%) and culture-negative-IE (15.9%, 13.4%, 9.9%) were more common in the younger patients. Valve surgery during admission was most frequent among patients <65 years (30.2%, 27.1%, 7%). Cumulative one-year mortality increased across ascending age groups (19.8%, 30,7%, 44,8%). The adjusted hazard ratios for one-year mortality were 1.58 (95% CI: 1.40–1.80, p<0.001) for patients aged 65–74 years and 2.40 (95% CI: 2.15–2.71, p<0.001) for patients aged ≥75 years, both compared with patients <65 years. The incidence of relapse bacteraemia did not differ significantly between age groups (3.3%, 3.1%, 3.3%). The main findings are summarized in Figure 1 (graphical abstract). Conclusion(s) Substantial age-related differences in IE were observed in this nationwide study. Older patients had a higher burden of cardiovascular comorbidities, cardiac devices, frailty, enterococcal infection, as well as substantially higher in-hospital and one-year mortality, while undergoing valve surgery less frequently. In contrast, younger patients exhibited a more heterogeneous comorbidity profile and a higher prevalence of S. aureus and CoNS IE. Taken together, these findings underscore the need for age-aware approaches to IE care, with implications for clinical practice, guideline development, and future research.