Changes in mammography screening in Ontario and Alberta following national guideline dissemination: an interrupted time series analysis.

Background: In November 2011, the Canadian Task Force on Preventive Health Care released guidelines for screening women at average breast cancer risk. Weak recommendations (framed using GRADE methodology) were made for screening women aged 50 to 74 years every two to three years, and for not screening women aged 40 to 49 years. Methods: We conducted an interrupted time series analysis using administrative data to examine bilateral mammography use before and after a national guideline dissemination strategy targeting primary care physicians. Women aged 40 to 74 years living in Ontario or Alberta from 30 th November 2008 to 30 th November 2014 were included. Strata included age, region of residence, neighbourhood income quintile, immigration status, and education level. Results: In both provinces, mammography use rates were lower in the post-intervention period (527 vs. 556 and 428 vs. 465/1000 participant-months - the monthly screening rate/1000 - in Ontario and Alberta, respectively). In Ontario, mammography trends decreased following guideline release to align with recommendations for women aged 40 to 74 (decrease of 2.21/1000 women, SE 0.26/1000, p<0.0001). In Alberta, mammography trends decreased for women aged 40 to 49 years (3/1000 women, SE 0.32, p<0.001) and 50 to 69 (2.9/1000 women, SE 0.79, p<0.001), but did not change for women aged 70 to 74 (0.7/1000 women, SE 1.23, p=0.553). In both provinces, trends in mammography use rates were sustained for up to three years after guideline release. Conclusions: The guideline dissemination strategy appeared to increase uptake of guideline-concordant screening practice in women aged 40 to 49 years in Ontario and Alberta and for women aged 50 to 74 years in Ontario. Further work is required to understand these findings and whether shared decision making about mammography between women and providers increased among women considering mammography.