Background
While the proportion of drug-use-associated infective endocarditis (DU-IE) has been increasing during the opioid crisis in the United States, it is unknown whether this is seen in Denmark, where several preventive means have been implemented. We aimed to assess the temporal proportion of DU-IE and examine the rate of IE recurrence and mortality.

Methods
This nationwide cohort study identified all patients with first-time infective endocarditis in 1999-2018. Drug use was defined using ICD-8/10 codes or prescription filling of medication for opioid use disorder. Long-term mortality was examined with a Kaplan-Meier estimator and a multivariate Cox model. The recurrence of IE was examined with the Aalen-Johansen method and a multivariate cause-specific hazard model.

Results
We included 8,843 patients with IE: 407 with DU-IE (60.7% male, median age 43.8 years) and 8,436 with non-DU-IE (65.8% male, median age 71.5 years). The proportion of DU-IE decreased from 5.9% to 3.8% during our study period. The one-year cumulative incidence of all-cause mortality was 16.9% (CI 12.9%-20.8%) for patients with DU-IE and 17.3% (CI 16.4%-18.2%) for patients with non-DU-IE. Drug use was associated with higher one-year mortality (adjusted HR 1.64 (CI 1.23%-2.21%)). The 1-year cumulative incidence of IE recurrence was 12.8% (CI 9.3%-16.3%) in patients with DU-IE and 4.3% (CI 3.8%-4.8%) in patients with non-DU-IE. Drug use was associated with a higher 1-year recurrence of IE (adjusted HR 3.39 (CI 2.35-4.88)).

Conclusion
In Denmark, the proportion of patients with DU-IE fell by one-third from 1999 to 2018. DU-IE was associated with higher mortality and recurrence rates than non-DU-IE.