The role of psychiatric-physical multimorbidity and continuity of care in seniors' medical emergency visits.

Multimorbidity contributes to complexity in seniors, but the impact of co-occurring physical and psychiatric illnesses on emergency department (ED) visits has received little attention. We investigated relationships between trans-diagnostic psychiatric severity, physical multimorbidity, and their interaction with non-psychiatric ED use; and tested the association of continuity of primary care on these relationships. A retrospective cohort design (n = 2,560,986) measured exposures to physical multimorbidity, psychiatric severity, and continuity in primary care. The main outcome was number of medical ED visits. At each level of physical multimorbidity, non-psychiatric ED visits increased with psychiatric severity. There were direct effects of physical multimorbidity (OR 1.35, 95%CI 1.35 - 1.35), psychiatric severity (OR 1.52, 95%CI 1.49 - 1.54), and continuity of care (low vs high OR 1.26, 95%CI 1.24 - 1.28) on frequent non-psychiatric ED use. Continuity of care did not mediate the relationships of physical multimorbidity, psychiatric severity or their interaction on frequent non-medical ED use. Transdiagnostic psychiatric severity correlates with seniors using the ED for non-psychiatric reasons, especially for repeated visits, in addition to the expected contribution of physical multimorbidity. Continuity of primary care does not mediate this relationship. Understanding the contribution of regular primary care requires further investigation.