Community prevalence of multimorbidity in Aotearoa New Zealand based on linked general practice and hospitalisation records.

AIM: The aim of this study was to quantify the community prevalence of multimorbidity from both hospital and general practice (GP) records. METHOD: Using encrypted health identifiers, electronic health record data from 374,071 patients aged ≥18 years, enrolled in ProCare primary health organisation in January 2014, were linked to national hospitalisation records. We identified the prevalence of multimorbidity (two or more long-term conditions [LTCs]) recorded within hospitalisation data (based on 61 ICD-10-AM LTC categories from the M3 multimorbidity index) and the same conditions matched to Read codes, Read terms or free text from GP records. RESULTS: Multimorbidity was identified in 31% of patients; under half of this group, 52,867 (14%), were identified from hospital records and 62,453 (17%) exclusively from GP records. Multimorbidity increased markedly with age, affecting over 60% of both sexes by 65-74 years. Under-estimation using hospitalisation data alone was greater for women, older people, Chinese and Europeans. CONCLUSION: Multimorbidity prevalence is substantially under-estimated if relying solely on hospital discharge data, capturing under half of the total multimorbidity burden found when GP-level data are included. These data sources need to be combined to properly recognise the complexity of care and health-system resources required to meet patient needs.