Multimorbidity in primary care: a systematic review of prospective cohort studies

Background: Primary care increasingly deals with patients with multimorbidity, but relevant evidence-based interventions are scarce. Knowledge about multimorbidity over time is required to inform the development of effective interventions. Aim: This review identifies prospective cohort studies of multimorbidity in primary care to determine: their nature, scope and key findings; the methodologies used; and gaps in knowledge. Design: Systematic review. Method: Studies were identified by searching electronic databases, reviewing citations, and writing to authors. Searches were limited to adult populations with no restrictions on publication date or language. In total, 996 articles were identified and screened. Results: Of the 996 articles, six detailing five completed prospective cohort studies were selected as appropriate. Three of the studies were undertaken in the US and two in The Netherlands; none was nationally representative. The main focus of the studies was: healthcare utilisation and/or costs (n = 3); patients' physical functioning (n = 1); and risk factors for developing multimorbidity (n = 1). The conditions that were included varied widely. The findings of these studies showed that multimorbidity increased healthcare costs (n = 2), inpatient admission (n = 1), death rates (n = 1), and service use (n = 3), and reduced physical functioning (n = 1). One study identified psychosocial risk factors for multimorbidity. No study used random sampling, sample sizes were relatively small (414-3745 patients at baseline), and study duration was relatively short (1-4 years). No study focused on prevalence, treatment use, patient safety, service models, cultural or socioeconomic factors, and patient experience, and no study collected qualitative data. Conclusion: Few longitudinal studies based in primary care have investigated multimorbidity. Further large, long-term prospective studies are required to inform healthcare commissioning, planning, and delivery.