Impact of multimorbidity on health care utilisation in Australian older adults aged 45 years and over: a large population-based data linkage cohort study

Background: Multimorbidity (MM), co-occurrence of two or more chronic health conditions in an individual, is often used in the assessment of complex healthcare needs and their impact on health outcomes. Management of MM is complex, but little is known about the impact of MM on health care services. Methods: We conducted a cross-sectional study among people aged 45+ years in New South Wales, Australia, who completed baseline questionnaires in the 45 and Up Study between 2005-2009. Baseline questionnaire data were linked to hospital, primary care Medicare billings, emergency department (ED), and deaths registry data. Our outcome of interest was high use of health care services within the 3-year baseline period (averaged over the years before, during and after recruitment). People who died during that period were excluded. High use was defined as: ≥11 General Practice (GP) visits, ≥2 ED visits, and ≥2 hospital admissions. Prevalence ratios (PRs) were used to measure the impact of MM, and Poisson regression models were used to estimate adjusted and unadjusted PRs with 95% confidence intervals. Results: Among 251,689 participants (46.5% male, and 46.1% aged