During the 10-year period of our study, the age-adjusted rate of hospitalization for CD declined (2
). The age-adjusted rate for UC was stable. Overall, hospitalization rates for UC were 40% to 50% of those for CD (2
). Hospitalized CD patients were more likely to be female and there was no sex differential in UC (2
). The peak age of hospitalization that occurred in the third decade mirrored the results of peak age of incidence of CD from elsewhere (14
Although there were some statistically significant disparities compared with the national average, overall, the ratio of CD to UC admissions, the rates of major surgery of all admissions and the readmission rates were mostly homogeneous across the country (2
). Recently, epidemiological data from five Canadian provinces, using the administrative definition of IBD validated previously, showed similar rates in Manitoba, Alberta and Saskatchewan for both CD and UC, with lower rates in British Columbia balancing out higher rates in Nova Scotia (13
). These data mirrored hospitalization trends for IBD among the provinces (1
). The relative uniformity across the country in these two reports suggests that the numbers of IBD patients across Canada and the likelihood that they will need hospitalization is consistent.
There was a rise in cases of colon cancer and rectal cancer among IBD and non-IBD patients. However, for those younger than 50 years of age, the RR was twofold among IBD versus non-IBD patients. This most likely reflects the known increased risk of colon cancer in IBD and rectal cancer in UC (16
), and colorectal cancer admissions would be uncommon among those younger than 50 years of age without a predisposing condition, such as IBD. The rates among IBD patients for those 50 years of age and older were, if anything, less than non-IBD patients.
The estimated prevalence of IBD in Canada during the later years of the study was approximately 150,000, and on that basis the rate of colon cancer diagnosis was approximately 0.1%. Previous estimates have ranged from 0.25% to 0.33% (9
) so the data in the present paper are in line with these previous figures. Furthermore, the entire population of IBD is likely not at risk for colon cancer. Patients with CD who have minimal or no colonic involvement are not at increased risk. The more shallow rise of rectal cancers over time may reflect that CD, which makes up more than 50% of the national population of IBD patients, is not associated with an increased risk for rectal cancer (9
Patients with IBD had relatively lower rates of both non-Hodgkin’s lymphoma and Hodgkin’s disease compared with non-IBD patients. These data support the notion that immunomodulatory drugs are not having a significant impact on increasing risk for lymphomas in IBD. Assuming that most patients with lymphoma get admitted to hospital even for one overnight stay over the course of their illness, the incidence of lymphoma was generally low and the rates over time were stable. There was an increase in the overall rate of non-Hodgkin’s lymphoma in both IBD and non-IBD patients after 2001/2002, which may be the result of more provincial jurisdictions switching to ICD-10-CA coding because there was no change in number of cases in those provinces that continued to report in ICD-9 or ICD-9-Clinical Modification. It is also not likely to be simply related to increased capture of hospital data because numbers of admissions for venous thromboembolism among non-IBD subjects steadily fell over time.
Older persons were more likely to have non-Hodgkin’s lymphoma. It has previously been reported that males with CD were significantly more likely to get non-Hodgkin’s lymphoma than the general population (9
) and these males on average were older at the age of presentation of CD than the general CD population. Hodgkin’s disease was uncommon in IBD, as opposed to what was reported in other studies (11
There was a trend toward increasing venous thromboembolism over time, including among young people. Overall, the prevalence of venous thromboembolism declined in non-IBD patients and plateaued in IBD patients. It is likely that most venous thromboembolic events were captured using hospital-based data because outpatient management of these events with subcutaneous heparins was much less common in the 1990s than in current practice. The increased RR of venous thromboembolism has been reported previously (10
). Overall, the rates of pulmonary emboli and venous thromboembolism were greater among IBD cases than the non-IBD population, but particularly among those younger than 50 years of age. While it is possible that physicians may be more likely to seek venous thrombosis diagnoses in IBD patients than in non-IBD patients, the increased RR of venous thrombosis in IBD versus non-IBD patients has been reported in a population-based sample. Furthermore, rates of venous thromboembolism appear to be rising in IBD but falling in non-IBD patients. This may reflect the increasing trend toward treating venous thromboembolism in the outpatient setting, whereas IBD patients may be acquiring their deep venous thromboembolism while already admitted to hospital (ie, during active inflammatory disease or postsurgically). These data add further support to encouraging clinicians to be more vigilant in providing prophylaxis against venous thrombosis in younger IBD patients when they are admitted.
Our study does have some significant limitations that require further explanation. First, our analysis was performed using administrative health care data collected from hospitals across Canada. Thus, the accuracy of our findings is in part dependent on the precision of diagnosis coding by the hospitals’ medical records personnel. Second, the HPOI database primarily concerns patients treated in acute care hospitals. Patients treated at a hospital but not admitted for an overnight stay were excluded, as well as those treated on an outpatient basis. Furthermore, the data in the present paper only capture patients diagnosed with these comorbidities who were hospitalized. It is reasonable to consider for all of the conditions in question that at least one hospitalization would have taken place. Certainly for colon and rectal cancer, at least one surgery admission would be expected. While the rates for colon and rectal cancer, pulmonary emboli and venous thromboembolism in IBD appeared to be rising, it was not possible to conclusively describe these changes because they may have been confounded by a number of factors, including reporting anomalies across provinces (12
). It is plausible that we have underestimated the numbers of lymphoma and Hodgkin’s disease diagnoses in any one year.