Temporal Trends of Adults Gaining or Losing Enrolment in Primary Care Medical Homes in Ontario, Canada: A Retrospective Serial Cohort Analysis.

Introduction Patient attachment to a primary care medical home has emerged as a key strategy to strengthen population health in high-income countries, including the U.S., Canada, New Zealand, the United Kingdom, and other European countries. In Canada, Ontario introduced primary care medical homes beginning in 2002, with capitation-based and interdisciplinary team-based models becoming increasingly prominent over time. Citing cost concerns, however, various government policies were subsequently introduced to limit physician entry into these types of medical homes. Entry into medical homes, remunerated mainly by fee-for-service and without funding for interdisciplinary teams, remained unrestricted. We sought to examine the dynamics of patients' attachment to a primary care medical home amidst this shifting policy landscape.  Methods We conducted a retrospective, population-level serial cohort analysis using linked health administrative datasets. We examined the monthly proportion of Ontario adults gaining or losing enrolment in a primary care medical home from 2009 to 2021. Temporal trends in net monthly enrolment gains/losses were assessed using linear regression, with statistical significance evaluated using a generalized additive mixed model accounting for temporal autocorrelation. The number of medical home physicians per capita over time was also examined. Unadjusted cross-sectional descriptive analyses at three time points (2009, 2014, and 2021) were conducted to characterize the sociodemographic profiles of adults gaining or losing enrolment. Results Initially, a larger proportion of adults were gaining rather than losing enrolment, but this gap narrowed over time. Medical home enrolment peaked at 77.3% (May 2015) and subsequently declined despite growth in physicians per capita practicing in medical homes. There was an overall statistically significant decline in net enrolment rates. After losing enrolment, patients experienced long durations without formal enrolment in a medical home (mean 57.5 months (SD 44.7)). Enrolment losses appeared to occur predominantly from fee-for-service-based medical homes and disproportionately affected equity-deserving populations. Conclusion Ontario's primary care medical home program did not achieve full population coverage, and policy changes limiting physician entry into capitation-based and interdisciplinary team-based medical homes occurred alongside a steady erosion in net enrolments. These dynamics may have impeded the full realization of the benefits of medical home enrolment at the health system level. Recent policy initiatives that remove previously implemented barriers to physician entry into capitation and team-based medical homes may help reverse this trend.