Associations of chronic disease and multimorbidity with healthcare utilization, mortality and adverse events in Estonia

Background: Multimorbidity is widespread, influencing disease progression and patient outcomes. Understanding the impact on the use of healthcare resources and healthcare associated harm is crucial for population-level interventions to reduce disease burden and improve quality of life. Methods: This retrospective study used administrative and clinical registry data from a 30% sample of the adult Estonian population. Multimorbidity was defined as ≥2 chronic diseases. Prevalence of chronic disease and multimorbidity was estimated among adults on January 1, 2024 (n = 324,942). Healthcare utilization included inpatient, outpatient, emergency visits, and prescription counts. Survival was assessed over five years following entry into multimorbidity strata (0-1, 2-4, 5-9, ≥10 conditions) in 2012-2024. We estimated 5-year risk of healthcare-associated harm diagnoses comparing patients with and without multimorbidity. Results: Chronic disease affected 60.3% of adults and multimorbidity 42.0%, increasing steeply with age. Multimorbidity was strongly associated with mortality, with adjusted hazard ratios of 1.61 (95% CI 1.57-1.66) for 2-4 conditions, 2.43 (2.36-2.51) for 5-9, and 3.35 (3.22-3.48) for ≥10 conditions compared with ≤1 condition. Healthcare utilization increased approximately linearly with each additional chronic disease, with 0.025 more inpatient visits, 0.034 emergency visits, 1.49 outpatient visits, and 4.04 prescriptions per person-year. Multimorbidity was also associated with higher risk of healthcare-associated adverse events, with up to sevenfold higher hazards for several complications, particularly related to procedural/surgical and prosthesis-related complications, including infections. Conclusion: Multimorbidity is prevalent in the Estonian population, increases mortality and healthcare use, and may increase healthcare-associated harm.