Background/Purpose:

Little is known about the influence of autoimmune inflammatory diseases on the risk of critical illness, as defined by Intensive care unit admissions (ICU). Using a large, population-based dataset we determined the incidence of ICU admissions in rheumatoid arthritis (RA), multiple sclerosis (MS) and inflammatory bowel disease (IBD). These conditions are highly prevalent in Western countries and often managed with immunomodulatory therapies.

Methods:

In a stable population of over 900,000 adults, hospital claims from an administrative database were linked to a population based ICU database to determine the incidence of ICU admissions from 2000-2010. RA, MS, and IBD patients were compared to cohorts from the general population, matched on sex, year of birth and region of residence, with up to 5 controls per case. Individuals with any diagnostic codes (ICD-9/10) for autoimmune inflammatory disease were excluded from the control cohorts. We used previously published and validated definitions for RA, MS, and IBD. Annual incidence rates were estimated by age group, sex, and geographic region (number of persons in each cohort with at ≥ 1ICU admission/ number of persons alive in that cohort at year-end).  Results were age and sex standardized to the general Canadian population. The incidence of ICU admission between the disease specific cohorts and matched cohorts were compared using incidence rate ratios (IRR). The 10 year cumulative incidence of ICU admission for the period 2000-2010 was compared: (number of persons with disease who had ≥ 1 episode of critical illness/ person-years at risk).  Hazard ratios for the 10 year period were calculated after adjustment for age, sex, socioeconomic status and comorbidity.

Results:

The annual incidence rates of ICU admission over the 10 year period were:  RA 0.82-1.18%; MS 0.51-1.07%; and IBD 0.55-1.12%, compared to the matched cohorts; 0.32-0.60%. The IRR for the 10 year cumulative incidence rate was 1.62 (95% CI 1.46-1.80) for RA; 1.54 (95% CI 1.30-1.77) for MS; 1.52 (95% CI 1.36-1.68) for IBD. Hazard ratios over the 10 year period for the 3 diseases were: RA HR=1.86 (95%CI 1.68-2.05); MS HR= 1.65 (95%CI 1.36-2.01); IBD HR= 2.02 (95%CI 1.78-2.28).          

Conclusion:   The risk of ICU admission is significantly increased in RA, MS and IBD patients compared to the general population. Close to 1% of adults with these diseases develop critical illness each year; representing a substantial cost to the healthcare system.  The risks between the 3 diseases are remarkably similar, suggesting shared risks from chronic inflammation and/or immunomodulatory therapy.