Evolving mortality rates in people who inject drugs: An Australian tertiary hospital observational study on infective endocarditis.

Background: Injection drug use (IDU) associated infective endocarditis (IE) is clinically challenging due to social issues this population endures. Rates of IDU are rising globally, however, there is a lack of clear guidelines for IDU associated IE. The aim of this study is to assess the epidemiology of the IDU and non-IDU populations and compare their long-term outcomes to help guide future management.

Methods: An observational cohort study was conducted on all 350 patients treated for IE at St Vincent's Hospital Melbourne between 1999 and 2015. Follow up was performed until death or January 2021. Primary outcome was all-cause mortality.

Results: IDU patients are younger (p<0.001), more likely to have concurrent infections (p<0.001), and other addiction disorders (p<0.001), while non-IDU patients are older with a higher level of comorbid illnesses (p<0.001). IDU and non-IDU patients received similar management during their admissions and experienced similar levels of in-hospital outcomes, except for non-IDU patient being more likely to develop pneumonia post-surgery (p = 0.03). IDU patients are more likely to become reinfected (p = 0.034) but have better long-term survival, with survival estimates at 15-years being 64.98% (95%CI: 50.94-75.92%) for IDU patients compared to 26.67% (95%CI: 19.76-34.05%) for non-IDU patients (p<0.001).

Conclusion: Despite having higher levels of reinfection, IDU patients have better long-term survival compared to non-IDU patients. Therefore, we suggest IDU patients should not have blanket restrictions on the management they are offered unless at the individual level there is a contraindication to therapy.