Understanding why substance-using patients seek care at emergency departments (EDs) and who utilizes such service at high rates is important in tailoring and targeting interventions. We conducted a retrospective/prospective cohort study of 326 medically ill substance-using adults to identify factors associated with 12-month high-frequency utilization of ambulatory care, ED, and inpatient medical care. The majority were actively using heroin (74.6%), cocaine (62.4%), and alcohol (54.4%); 94.8% had a chronic medical condition; and 53.8% reported a chronic mental health condition. High-frequency use of ED (≥ 3 visits) was independently associated with being female (adjusted odds ratio [AOR] = 1.88; 95% confidence interval [95% CI] = 1.12, 3.17), being African American (AOR = 2.36; 95% CI = 1.30, 4.29), being homeless (AOR = 2.07; 95% CI = 1.08, 3.96), a history of > 1 substance abuse treatment episode (AOR = 4.10; 95% CI = 3.28, 10.87), and ≥ 1 ambulatory care visit (AOR = 8.94; 95% CI = 3.28, 24.41). However, the combination of having certain chronic conditions (seizure disorder, hepatitis B, and hepatitis C) and accessing ambulatory care was protective against high-frequency use of ED. In contrast, high-frequency use of ambulatory care (≥ 3 visits) was independently associated with having insurance (Medicare/Medicaid: AOR = 2.39; 95% CI = 1.31, 4.69), having HIV/AIDS (AOR = 3.15; 95% CI = 1.70, 5.85), and receiving substance abuse treatment during the study period (AOR = 3.58; 95% CI = 1.61, 7.98) Efforts to redirect medical care to more subacute settings will likely require both capacity building and addressing a client's underlying needs, including homelessness, access to substance abuse treatment, and chronic disease management.
