The goal of this observational study is to improve the understanding of infective endocarditis by investigating clinical characteristics, treatment strategies, and short- and long-term outcomes in patients diagnosed with infective endocarditis in Sweden. The study includes all adults >18 years of age diagnosed with infective endocarditis in Sweden since 1997 through linkage of nationwide Swedish health data registers within the Endocarditis Clinical Awareness, Research and Evaluation in Sweden (ENDO-CARE) project. For each patient, four individuals from the general population matched on age and sex are included as population comparators.

The main questions it aims to answer are:

• Which patients with infective endocarditis benefit from valve surgery, and what is the optimal timing of surgery?
• Which patient-, disease-, microbiological-, and socioeconomic factors are associated with short- and long-term outcomes, including mortality, recurrent infective endocarditis, heart failure, stroke, and other major complications?
• How do long-term outcomes and life expectancy differ between patients with infective endocarditis and matched individuals from the general population?
• How have the incidence, management, microbiology, and outcomes of infective endocarditis changed over time?

Researchers will compare surgically and non-surgically treated patients, different clinical subgroups, and patients with infective endocarditis with matched population comparators to identify factors associated with treatment decisions, prognosis, and long-term outcomes.

Participants will not undergo any study-specific interventions or examinations. The study is based on linkage of existing nationwide Swedish health care and population registers, including data on hospital admissions, cardiac surgery, microbiology, prescribed medications, dental care, socioeconomic factors, and causes of death.

Infective endocarditis (IE) is a rare but life-threatening disease associated with high morbidity and mortality despite advances in diagnostic methods, antimicrobial therapy, and cardiac surgery. Although current international guidelines provide recommendations concerning management of patients with infective endocarditis, many important clinical questions remain unanswered because randomized clinical trials are difficult to perform in this patient population. Consequently, most evidence is derived from observational studies, which are often limited by small sample sizes, selected patient populations, and relatively short follow-up.

The Endocarditis Clinical Awareness, Research and Evaluation in Sweden (ENDO-CARE) project is a nationwide research platform established to improve the understanding of infective endocarditis through comprehensive linkage of Swedish national health data registers. The ENDO-CARE database includes all patients diagnosed with infective endocarditis in Sweden since 1997. In addition, four matched individuals from the general population are included for each patient to enable comparisons of long-term outcomes and life expectancy with the background population.

The database integrates information from multiple nationwide registers, including hospital admissions, diagnoses, cardiac surgery, microbiology, echocardiographic findings, prescribed medications, socioeconomic factors, dental care, causes of death, and other population-based health registers. Individual-level linkage is performed using the unique Swedish personal identity number before data are pseudonymized for research purposes.

The overall objective of ENDO-CARE is to broaden the knowledge about endocarditis and to improve the evidence base for the management of infective endocarditis. Planned studies will investigate patient characteristics, microbiology, cardiac imaging findings, treatment strategies, and both short- and long-term outcomes.

Particular emphasis will be placed on:

• Evaluating indications for and timing of valve surgery
• Identifying patient groups that benefit most from surgical intervention
• Assessing temporal trends in incidence and management
• Investigating prognostic factors and risk stratification
• Evaluating long-term survival and life expectancy
• Studying disparities in care related to sex, age, and socioeconomic status.

The ENDO-CARE platform is designed to support multiple observational studies using modern epidemiological methods. The comprehensive nationwide design minimizes selection bias, enables complete follow-up through national registers, and allows the study of rare patient subgroups and clinically important outcomes that cannot readily be evaluated in randomized clinical trials.

The knowledge generated through ENDO-CARE is expected to improve risk stratification, support clinical decision-making regarding medical and surgical treatment, inform future national and international clinical guidelines, and ultimately contribute to more individualized and equitable care for patients with infective endocarditis.

Inclusion Criteria:

• Patients aged >18 years diagnosed with infective endocarditis in Sweden from January 1, 1997, and onwards, identified through nationwide Swedish health data registers.
• Individuals from the general population matched to patients with infective endocarditis (four comparators per patient) on age and sex.

Exclusion Criteria:

• Individuals with missing or invalid personal identity numbers precluding linkage between national registers.
• Individuals with incomplete or inconsistent registry information preventing determination of study eligibility or follow-up, where applicable to specific analyses.

The study population is derived from the Swedish National Patient Register and includes all patients diagnosed with infective endocarditis who received care within the Swedish healthcare system. Using the unique personal identity number assigned to all Swedish residents, several nationwide Swedish health data registers has been cross-linked to obtain further information about baseline characteristics including socioeconomic information, cardiac surgery, endocarditis specific information such as microbiology, cardiac imaging and prescribed antibiotics, survival status and hospital admissions during follow-up.

For each patient with infective endocarditis, four matched individuals from the general Swedish population are identified through the Swedish Population Register to serve as population comparators.

The data underlying this database cannot be shared publicly due to data protection regulations.