Patient clustering in primary care settings: Outcomes and quality of care.

Objective: To determine whether neighbours who share the same family physicians have better cardiovascular and health care outcomes.

Design: Retrospective cohort study using administrative health databases.

Setting: Ontario.

Participants: The study population included 2,690,482 adult patients cared for by 1710 family physicians.

Interventions: Adult residents of Ontario were linked to their family physicians and the geographic distance between patients in the same panel or list was calculated. Using distance between patients within a panel to stratify physicians into quintiles of panel proximity, physicians and patients from close-proximity practices were compared with those from more-distant-proximity practices. Age- and sex-standardized incidence rates and hazard ratios from cause-specific hazards regression models were determined.

Main Outcome Measures: The occurrence of a major cardiovascular event during a 5-year follow-up period (2008 to 2012).

Results: Patients of panels in the closest-proximity quintile lived an average of 3.9 km from the 10 closest patients in their panel compared with 12.4 km for the 10 closest patients of panels in the distant-proximity quintile. After adjusting for various patient and physician characteristics, patients in the most-distant-proximity practices had a 24% higher rate of cardiovascular events (adjusted hazard ratio=1.24 [95% CI 1.20 to 1.28], <.001) than patients in the closest-proximity practices. Age- and sex-standardized all-cause mortality and total per patient health care costs were also lowest in the closest-proximity quintile. In sensitivity analyses restricted to large urban communities and to White long-term residents, results were similar.

Conclusion: The better cardiovascular outcomes observed in close-proximity panels may be related to a previously unrecognized mechanism of social connectedness that extends the effectiveness of primary care practitioners.