摘要：Objectives. To assess longitudinal patterns of community health center (CHC) utilization and the effect of insurance discontinuity after Oregon’s 2008 Medicaid expansion (the Oregon Experiment). Methods. We conducted a retrospective cohort study with electronic health records and Medicaid data. We divided individuals who gained Medicaid in the Oregon Experiment into those who maintained (n = 788) or lost (n = 944) insurance coverage. We compared these groups with continuously insured (n = 921) and continuously uninsured (n = 5416) reference groups for community health center utilization rates over a 36-month period. Results. Both newly insured groups increased utilization in the first 6 months. After 6 months, use among those who maintained coverage stabilized at a level consistent with the continuously insured, whereas it returned to baseline for those who lost coverage. Conclusions. Individuals who maintained coverage through Oregon’s Medicaid expansion increased long-term utilization of CHCs, whereas those with unstable coverage did not. Policy implications. This study predicts long-term increase in CHC utilization following Affordable Care Act Medicaid expansion and emphasizes the need for policies that support insurance retention. The Affordable Care Act (ACA) provided Americans with new access to health insurance, 1 and many policymakers predicted a subsequent increase in health care utilization. 2–4 Early studies since the ACA’s implementation confirm this increase. 5–7 However, important questions remain about where newly insured individuals will get care, how trends in utilization will evolve over time, and how discontinuity of insurance will have an impact on utilization. 8,9 These important questions will guide allocation of resources and development of needed infrastructure and workforce to meet the primary care demands of a growing population of insured patients. Ensuring access to primary care for the newly insured is critical to optimizing public health and has proven challenging with previous Medicaid expansions. 3,10 Because long-term data from the ACA are not yet available, previous insurance expansions must inform predictions of the ACA’s impact on long-term utilization of primary care. Past studies of policy-driven expansions demonstrate how care-seeking behaviors change when a previously uninsured population receives coverage. 11–14 In Massachusetts, a 2006 insurance expansion resulted in increased utilization among the newly insured, 3,15,16 and community health centers (CHCs) saw utilization increase by 31%. 17 After the 2008 Oregon Experiment Medicaid expansion, ambulatory care utilization increased 18–20 and use of CHC services increased by 22% in the first year. 21 Individuals who gained Medicaid coverage through the Oregon Experiment subsequently had 39% more CHC visits than those who did not gain coverage. 22 We describe trends in CHC utilization for 36 months after Oregon’s 2008 Medicaid expansion to (1) investigate longitudinal utilization patterns, (2) observe the extent to which those gaining coverage experienced subsequent loss in coverage, and (3) better understand the extent to which a coverage loss affected utilization in subsequent years. Although we did not seek to estimate the causal effect of insurance coverage on primary care utilization as have others, 22 this longitudinal investigation of insurance cohorts adds to previous studies reporting that even short coverage gaps can have significant effects on access to care and utilization. 23–27 The use of new electronic health record (EHR) data sources enabled us to overcome some of the biases reported in past studies that used self-report (i.e., nonresponse bias, recall bias). Furthermore, unlike insurance claims data commonly used for tracking utilization rates, EHR data capture utilization among patients gaining and then losing insurance coverage and also allow for inclusion of an uninsured comparison group.
