Asthma is not associated with the need for surgery in Crohn’s disease when controlling for smoking status: a population-based cohort study

Abstract

M Ellen Kuenzig,1–3 Mohsen Sadatsafavi,4 J Antonio Aviña-Zubieta,5 Rebecca M Burne,6 Michal Abrahamowicz,6,7 Marie-Eve Beauchamp,7 Gilaad G Kaplan,8–11,* Eric I Benchimol1–3,12,13,* 1Children’s Hospital of Eastern Ontario (CHEO) Inflammatory Bowel Disease Centre, Division of Gastroenterology, Hepatology and Nutrition, Children’s Hospital of Eastern Ontario, Ottawa, ON, Canada; 2Health Information Technology Program, CHEO Research Institute, Ottawa, ON, Canada; 3Institute for Clinical Evaluative Sciences, Ottawa, ON, Canada; 4Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC, Canada; 5Arthritis Research Canada, Division of Rheumatology, University of British Columbia, Vancouver, BC, Canada; 6Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, QC, Canada; 7Centre for Health Outcomes Research (CORE), Research Institute of the McGill University Health Centre, Montreal, QC, Canada; 8Department of Medicine, University of Calgary, Calgary, AB, Canada; 9Department of Community Health Sciences, University of Calgary, Calgary, AB, Canada; 10O’Brien Institute for Public Health, University of Calgary, Calgary, AB, Canada; 11Snyder Institute for Chronic Diseases, University of Calgary, Calgary, AB, Canada; 12Department of Pediatrics, University of Ottawa; Ottawa, ON, Canada; 13School of Epidemiology and Public Health, University of Ottawa, Ottawa, ON, Canada *These authors contributed equally to this work Purpose: Growing evidence suggests asthma and Crohn’s disease commonly cooccur. However, the impact of asthma on the prognosis of Crohn’s disease is unknown. The aim of our study was to assess the effect of asthma on the need for intestinal resection in patients with Crohn’s disease while adjusting for smoking status, imputed from a smaller, secondary data set. Patients and methods: Using health administrative data from a universally funded healthcare plan in Alberta, Canada, we conducted a cohort study to assess the effect of asthma on the need for surgery in patients with Crohn’s disease diagnosed between 2002 and 2008 (N=2,113). Validated algorithms were used to identify incident cases of Crohn’s disease, cooccurring asthma, and intestinal resection. The association between asthma and intestinal resection was estimated using multivariable Cox proportional hazards regression. Smoking status was imputed using a novel method using martingale residuals, derived from a data set of 485 patients enrolled in the Alberta Inflammatory Bowel Disease Consortium (2007 to 2014) who completed environmental questionnaires. All analyses were adjusted for age, sex, rural/urban status, and mean neighborhood income quintile. Results: Asthma did not increase the risk of surgery in the health administrative data when not adjusting for smoking status (HR 1.03, 95% CI 0.81 to 1.29). The association remained nonsignificant after imputing smoking status in the health administrative data (HR 1.03, 95% CI 0.81 to 1.29). Conclusion: Although asthma is associated with an increased risk of Crohn’s disease, co-occurring asthma is not associated with the risk of surgery in these patients. This null association persisted after adjusting for smoking status. This study described a novel method to adjust for confounding (smoking status) in time-to-event analyses, even when the confounding variable is unmeasured in health administrative data. Keywords: Crohn’s disease, asthma, surgery, unmeasured confounding, health administrative data

Keywords

• Crohn’s disease
• asthma
• surgery
• unmeasured confounding
• health administrative data