The management of IBD continues to evolve rapidly, but temporal trends in population-level mortality have not been previously reported. In-hospital mortality is an important clinical outcome readily available through nationally representative data (as opposed to ambulatory outcomes, for which nationally representative data are not readily available). In this study, we found that, over the 13-year period from 1994 to 2006, the odds of in-hospital mortality among hospitalizations associated with IBD decreased by 17% per time period studied in analysis adjusted for age and comorbidity. These trends seem to be driven largely by hospitalizations associated with ulcerative colitis. Adjusted analyses suggest that trends are not likely explained by temporal changes in age or comorbidity.
Prior studies of in-hospital mortality for patients with IBD used samples collected through the Nationwide Inpatient Sample ranging from 1998 to 2005. These studies reported point estimates of in-hospital mortality, but did not examine temporal trends in in-hospital mortality [3
]. Mortality rates for unselected IBD patients in these studies ranged from 0.3 to 1.3% of hospital admissions, or 0.6 to 1.2 deaths per 1,000 hospital days. We found similar mortality rates, supporting the accuracy of our primary outcome measure. Most patients who died in our study were age 60
years or older. This is consistent with prior studies, which showed that IBD confers a markedly increased mortality risk among patients age 60
years and older [12
Although our data do not permit exact identification of driving forces behind these trends, they do permit some speculation. Our analyses were adjusted for age and comorbid status, using the Charlson index, which is known to be an accurate measure of comorbidities. The fact that time period remained significantly associated with mortality suggests that reductions in mortality are not primarily due to confounding by temporal trends in age or comorbidity among hospitalizations included in the NHDS. The NHDS uses a similar sampling protocol each year, so our results are not likely confounded by measurement bias. Furthermore, it is unlikely that the disease process of IBD itself changed dramatically over the 13
year time-period of our study.
The above factors lead to natural speculation that improvements in healthcare could contribute to reductions in in-hospital mortality. Our sensitivity analyses allow some commentary in three specific areas. The sensitivity analysis limited to hospitalizations with a primary diagnosis of IBD suggests that an improvement in IBD care alone is not likely to account for reductions in mortality. However, this analysis included a small number of deaths (59 deaths) spread out over a 13-year period, limiting the power of the analysis. Improvements in IBD care would probably be better assessed in an ambulatory setting. The sensitivity analysis excluding hospitalizations with a primary diagnosis of cardiopulmonary disease suggests that improved care for cardiopulmonary diseases is not the sole driver of reductions in mortality. Finally, the sensitivity analysis excluding brief hospitalizations suggests that trends are not likely due more frequent hospitalizations for less ill patients, who would likely have brief hospitalization durations. It is likely than numerous factors contribute to the mortality trends that we document. Importantly, though, our analyses argue against confounding by changing age, comorbidity, or hospitalization practices.
It is interesting that mortality trends among IBD-associated hospitalizations appeared to be driven primarily by hospitalizations associated specifically with ulcerative colitis. Although ulcerative colitis accounted for only a third of IBD-associated hospitalizations, more than half of deaths were in hospitalizations with ulcerative colitis, and ulcerative colitis conferred a 41% increased odds of death compared with Crohn’s disease. Furthermore, mortality reduced significantly over time in all IBD hospitalizations, and in ulcerative colitis hospitalizations specifically, but not in Crohn’s disease hospitalizations. Compared with Crohn’s disease, hospitalizations with ulcerative colitis were associated with a significantly higher mean age and Charlson index, but these did not vary over time in ulcerative colitis related hospitalizations (data not shown). Furthermore, the proportion of ulcerative colitis associated hospitalizations with a primary (versus secondary) diagnosis of IBD did not change over time (data not shown).
A major impetus for this study was the lack of studies documenting temporal trends in IBD-related outcomes. We chose to use inpatient data due to the lack of nationally representative ambulatory data for patients with IBD. Much of what we know about the course of IBD is drawn from cohorts that, while well-characterized, are not nationally representative [13
]. This limits understanding of changes in IBD course over time at a population level, and underscores the need for prospectively collected, nationally representative, ambulatory data in IBD.