Survival Comparison of Patients With Cystic Fibrosis in Canada and the United States: A Population-Based Cohort Study

Abstract

Background: In 2011, the median age of survival of patients with cystic fibrosis reported in the United States was 36.8 years, compared with 48.5 years in Canada. Direct comparison of survival estimates between national registries is challenging because of inherent differences in methodologies used, data processing techniques, and ascertainment bias.

Objective: To use a standardized approach to calculate cystic fibrosis survival estimates and to explore differences between Canada and the United States.

Design: Population-based study.

Setting: 42 Canadian cystic fibrosis clinics and 110 U.S. cystic fibrosis care centers.

Patients: Patients followed in the Canadian Cystic Fibrosis Registry (CCFR) and U.S. Cystic Fibrosis Foundation Patient Registry (CFFPR) between 1990 and 2013.

Measurements: Cox proportional hazards models were used to compare survival between patients followed in the CCFR (n = 5941) and those in the CFFPR (n = 45 448). Multivariable models were used to adjust for factors known to be associated with survival.

Results: Median age of survival in patients with cystic fibrosis increased in both countries between 1990 and 2013; however, in 1995 and 2005, survival in Canada increased at a faster rate than in the United States (P < 0.001). On the basis of contemporary data from 2009 to 2013, the median age of survival in Canada was 10 years greater than in the United States (50.9 vs. 40.6 years, respectively). The adjusted risk for death was 34% lower in Canada than the United States (hazard ratio, 0.66 [95% CI, 0.54 to 0.81]). A greater proportion of patients in Canada received transplants (10.3% vs. 6.5%, respectively [standardized difference, 13.7]). Differences in survival between U.S. and Canadian patients varied according to U.S. patients' insurance status.

Limitation: Ascertainment bias due to missing data or nonrandom loss to follow-up might affect the results.

Conclusion: Differences in cystic fibrosis survival between Canada and the United States persisted after adjustment for risk factors associated with survival, except for private-insurance status among U.S. patients. Differential access to transplantation, increased posttransplant survival, and differences in health care systems may, in part, explain the Canadian survival advantage.

Primary funding source: U.S. Cystic Fibrosis Foundation.

Figure 1. (A) Median Survival Age using a 5-year rolling window, Canada vs. USA, 1990 to 2013; (B) Difference in Median Age of Survival between Canada and the USA, 1990-2013

Figure 2. Creation of Study Cohort for Multivariable Analysis (2009-2013)

Figure 3. Unadjusted univariate sub-group analysis comparing the risk of death in the Canada vs. US (2009-2013)