Primary care effectiveness, multimorbidity, and hospital use in public and private health-care systems in Brazil: a cross-sectional analysis of data from the 2019–2021 Brazilian longitudinal study of aging

Background Whether patient-reported experiences in primary care modify the association between multimorbidity and emergency department (ED) visits and hospitalizations remains unclear. We examined these associations across public and private health system sectors among Brazilians aged ≥50 years. Methods This cross-sectional study used nationally representative data from the 2019–2021 Brazilian Longitudinal Study of Aging. Multimorbidity was defined as the presence of ≥2 of 13 chronic conditions. A 12-item patient-reported primary care effectiveness index captured access, continuity, communication, and coordination with participants' usual source of healthcare. Primary outcomes were ED visits and hospitalizations in the past 12 months. Poisson regression models estimated associations with the outcomes, and assessed interactions among multimorbidity, primary care effectiveness, and health system sectors. Findings Among 9058 participants (mean age=66.3 ± 9.9 years; females=55.3%; White race/ethnicity = 46.4%), 38.0% had multimorbidity. Overall, 12.5% reported an ED visit and 6.0% ≥ 1 hospitalization in the past 12 months. Multimorbidity was associated with approximately twice the prevalence of ED visits and three times the prevalence of hospitalizations. Primary care effectiveness modified these associations across health system sectors (three-way interaction p=0.04 for ED visits and p < 0.001 for hospitalization). In the public system, higher primary care effectiveness attenuated the association between multimorbidity and hospitalization (interaction prevalence ratio [PR] = 0.74, 95% confidence interval [CI] = 0.63–0.87). In contrast, in the private system, higher primary care effectiveness strengthened the associations of multimorbidity with ED visits (interaction PR=1.40, 95% CI=1.18–1.66) and hospitalization (interaction PR=1.75, 95% CI=1.22–2.50). Interpretation Associations between multimorbidity and healthcare use varied according to patient-reported primary care experiences and health system sector. Funding The Brazilian National Council for Scientific and Technological Development, the Alzheimer's Association, and the National Institute on Aging.