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Angela Forbes, MPH 2013



Inflammatory bowel disease (IBD) is a chronic medical condition that has symptoms including diarrhoea, weight loss and fatigue. There are two common phenotypes of IBD: Crohn's disease and ulcerative colitis. Historically the disease resulted in high mortality rates directly through severe disease and inflammation, but in current times death rates have fallen due to effective medications and surgical interventions. Recent international research has shown the mortality rates for IBD patients still remain slightly above those of the general population. IBD mortality may potentially occur through several pathways including malignancies occurring because of sustained inflammation or as a result of using immunosuppressant medications. To date there are not any current population-based studies on IBD mortality from the Southern Hemisphere so this research will provide this information.


This research evaluates the mortality and survival of IBD patients in Canterbury, New Zealand. The aims include determining what patients died from, and if particular patient characteristics lead to an increased risk of death. To achieve these aims patient deaths are compared with death rates in the general population and with a group of control participants.


This investigation is an observational study following a closed cohort of IBD patients who were recruited in 2005. Death information was collected from medical records for those participants who died over the 7 year follow-up period. The study was population-based using a group of 1420 IBD patients recruited in Canterbury for a previous epidemiological study. The patients included both incident and prevalent cases. 598 control participants recruited at the same time in 2005, were also followed as a comparison group. Date and cause of death was established using patient identifiers to search Christchurch hospital records, and use of the National Mortality Collection enabled patients who died outside of Canterbury to be identified.  


133 IBD patients (9%) and 20 control participants (3%) died during the 7 year study period. Standardised mortality ratios were used to compare the observed deaths with those expected in the general New Zealand population. Crohn's disease patients had a significantly increased risk of dying from all causes 1.69 (1.30, 2.17). The estimated all cause risk for ulcerative colitis patients was slightly increased compared to the general population and not statistically significant 1.24 (0.97, 1.56). The cause of death analysis showed IBD patients were at increased risk of digestive diseases, digestive cancers and respiratory diseases. Survival analysis showed the IBD patients had an increased risk of mortality compared with the control participants in crude and adjusted analyses. Controlling for age, prior liver disease, cancer, smoking and a higher number of sick days in the previous year, were significant predictors of mortality.


The pattern of significantly increased mortality for Crohn's disease patients and uncertainty about whether there is an increase in mortality for ulcerative colitis patients reflects the findings of other international studies. The main strength of this research is the large sample of IBD patients and the stable population they were drawn from. The main limitation of the study is the way the death information was gathered for the control participants, which potentially underestimates the number of control deaths. To reflect the potential areas of lesser quality and the small number of deaths, the analysis focused on high level outcomes rather than detailed causes of death, or control and patient comparisons. The results may be used to reassure patients that most of the IBD deaths occur in older aged individuals as is observed in the general population. It is recommended that future investigations look at mortality outcomes over longer time periods, and determine if New Zealand specific mortality patterns can be identified.

Supervisors: Professor Phillip Schluter and Associate Professor Richard Gearry

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