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. Design Retrospective cohort analysis. Setting All residents in the province of Alberta, Canada registered with the Alberta Health Care Insurance Plan population registry. Participants 497362 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 chi(2) 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.