Existing comorbidities in people with osteoarthritis: a retrospective analysis of a population-based cohort in Alberta, Canada.

Objectives: The purpose of this study is to estimate the prevalence of comorbidities among people with osteoarthritis (OA) using administrative health data.

Design: Retrospective cohort analysis.

Setting: All residents in the province of Alberta, Canada registered with the Alberta Health Care Insurance Plan population registry.

Participants: 497 362 people with OA as defined by 'having at least one OA-related hospitalization, or at least two OA-related physician visits or two ambulatory care visits within two years'.

Primary Outcome Measures: We selected eight comorbidities based on literature review, clinical consultation and the availability of validated case definitions to estimate their frequencies at the time of diagnosis of OA. Sex-stratified age-standardised prevalence rates per 1000 population of eight clinically relevant comorbidities were calculated using direct standardisation with 95% CIs. We applied χ tests of independence with a Bonferroni correction to compare the percentage of comorbid conditions in each age group.

Results: 54.6% (n=2 71 794) of people meeting the OA case definition had at least one of the eight selected comorbidities. Females had a significantly higher rate of comorbidities compared with males (standardised rates ratio=1.26, 95% CI 1.25 to 1.28). Depression, chronic obstructive pulmonary disease (COPD) and hypertension were the most prevalent in both females and males after age-standardisation, with 40% of all cases having any combination of these comorbidities. We observed a significant difference in the percentage of comorbidities among age groups, illustrated by the youngest age group (<45 years) having the highest percentage of cases with depression (24.6%), compared with a frequency of 16.1% in those >65 years.

Conclusions: Our findings highlight the high frequency of comorbidity in people with OA, with depression having the highest age-standardised prevalence rate. Comorbidities differentially affect females, and vary by age. These factors should inform healthcare programme and delivery.