Introduction: Studies have examined the seasonality of inflammatory bowel disease (IBD) disease onset and activity. Patterns suggest greater likelihood of disease remission in the summer and disease exacerbation in the winter. It is unknown whether IBD mortality trends follow a similar pattern. In this study, we investigated seasonal variations in IBD mortality and the impact of the pandemic on these trends. Methods: Using the National Vital Statistics System data set through the CDC WONDER website, data on IBD-related deaths among U.S. adults aged 25 years and older was obtained. IBD was defined as Crohn’s disease or ulcerative colitis based on ICD-10 codes. Age-standardized mortality rates (ASMRs) per 100,000 persons were calculated for all-cause, non-COVID-related, and COVID-related mortality in this population. Number of monthly COVID-19 cases in the general population were also obtained from the CDC website. Seasons were defined as winter (December to February), spring (March to May), summer (June to August), and fall (September to November). Winter’s year was defined using the year of December (i.e. Winter 2010 = December 2010 to February 2011). Mann-Whitney tests were performed to compare the median all-cause ASMRs of summer and winter pre-pandemic (prior to Winter 2019) and during the pandemic (Winter 2019 and beyond). Results: From January 2010 to December 2021, there were 34,648 IBD-related deaths, 3,242 (9.35%) of which occurred during the pandemic. Pre-pandemic, IBD mortality demonstrated peaks in winter and nadirs in summer (Figure). In fact, as seen in Table, median all-cause ASMR was significantly higher in winter compared to summer pre-pandemic (0.3484 vs 0.3144, p< 0.0001). In Winter 2020, there was still a peak in IBD-related mortality, but this was largely driven by COVID-19-related death (Figure). However, over the duration of the pandemic, the median all-cause mortality of winter versus summer ceased to be significantly different (0.4371 vs 0.4202, p >0.999) (Table). Conclusion: Using a nationwide dataset, we identified seasonal variation in IBD mortality rates, with peaks in winters and nadirs in summers. However, this trend was less apparent during the COVID-19 pandemic. Further investigation into why there is seasonal variation in IBD mortality is warranted, including why seasonal trends were disrupted during the pandemic.Figure 1.: All-Cause, Non-COVID-Related and COVID-Related Age-Standardized Mortality Rates Among IBD Decedents from 2010 to 2021 with Overall COVID-19 Case Numbers. Trends in ASMR per 100,000 persons are shown among all IBD decedents. COVID-19 case numbers are shown among all individuals in the U.S. ASMR=Age-Standardized Mortality Rate. COVID=coronavirus disease. IBD=inflammatory bowel disease. Summer=June-August. Winter=December-February. Table 1. - Difference in Median All-Cause ASMR in Summer and Winter Pre-Pandemic and During Pandemic Median All-Cause ASMR per 100,000 Persons Summer Winter P-Value Pre-Pandemic 0.3144, n=9 0.3484, n=9 < 0.0001 During Pandemic 0.4202, n=2 0.4371, n=2 > 0.9999 P-Values obtained by Mann-Whitney test. ASMR per 100,000 persons are shown among all IBD decedents. Summer=June-August. Winter=December-February. Pre-Pandemic=Summer 2010-Winter 2019. During Pandemic=Winter 2019-Summer 2021.
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