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Seasonal Patterns of Inflammatory Bowel Disease in the United States: Consistency in Admission Rates
John V. Gahagan*, Katherine Stern, Matthew Whealon, Alessio Pigazzi, Joseph C. Carmichael, Michael J. Stamos, Steve Mills
Surgery, UC Irvine Health, Orange, CA
Introduction:
Several previous international studies have reported a peak in the incidence of inflammatory bowel disease (IBD) during the spring and summer. However this relationship has not been well established. The purpose of this study was to evaluate the variation by season in admissions and need for surgical intervention of IBD patients in the United States.
Methods: A retrospective review of the Nationwide Inpatient Sample (NIS) database was performed to identify all patients admitted with a principle diagnosis of Crohn's disease (CD) or Ulcerative Colitis (UC) from 2010-2012. Patients were stratified by admission quarter (Q1-Q4). Multivariate analysis was used to identify associations between patient characteristics and admission quarter.
Results:
A total of 189,339 IBD admissions were identified during the study period: 120,569 for CD and 68,770 for UC. Admissions were evenly distributed among seasons, with approximately 30,000 CD admissions and 17,000 UC admissions per season. Admission characteristics including rates of emergency admission (39% for CD and 36% for UC), teaching hospital status (51% for CD, 53% for UC), and hospital location (89% urban for CD, 90% for UC) were also similar among the seasons. Patient characteristics were generally uniform among the seasons, although there were some statistical differences in the rates of chronic pulmonary disease, hypothyroidism, obesity, peripheral vascular disease, and renal failure. However, there were no clear seasonal patterns in these differences. On multivariate analysis, patients under the age of 30 (OR 1.05; 95%CI 1.01, 1.09) and smokers (OR 1.07; 95%CI 1.03) were more likely to be admitted in Q2 compared to Q1. Males were more likely to be admitted in Q4 compared to Q1 (OR 1.04; 95%CI 1.01, 1.07). There was a statistically significant difference in the proportion of CD patients who underwent an operation in Q2 (23.41%) and Q4 (23.79%) vs. Q1 (22.69%) and Q3 (22.55%) (p<0.05). For UC, approximately 24% of patients underwent an operation during admission, without a statistical difference among seasons.
Conclusions:
This study does not show a seasonal variation is the incidence of IBD admissions. The international reports of seasonal variation of the incidence of IBD occurred in small and more geographically homogenous countries, with less variability of climate and weather patterns during the seasons across the country. The United States has many diverse climates and variation in the seasonal weather patterns. Previously reported seasonal variation of the incidence of IBD may be associated with season specific factors that are not consistent throughout the United States. Noted differences in need for surgery may also be amplified in regions with distinct seasonal weather patterns.
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