BACKGROUND:
Multimorbidity is an escalating challenge for health systems worldwide. In Chile, a high-income country experiencing sustained migration, evidence shows that migrants face lower levels of health system affiliation and greater barriers to care compared to locals. These may shape their vulnerability to developing multimorbidity. However, limited research has examined whether migration status interacts with healthcare access and high multimorbidity (10+ chronic conditions, Chua, 2021). We explored the association between sociodemographics, healthcare access, and high multimorbidity, with focus on the interaction effect of healthcare affiliation among migrants and Chileans.

METHODS:
We conducted a cross-sectional study of 1,759 adults (760-migrants/999-Chileans) using confidential primary data collected in three low-income boroughs in Santiago. Bivariate analyses were performed, followed by a multivariable logistic regression model adjusted for sex, age, employment status, registration at a health center, and self-reported access barriers. An interaction term between migration status and healthcare affiliation was included. Adjusted marginal probabilities and standard model performance indicators were estimated. Ethical approval and informed consent were obtained (FondecytRegular#1201461/ANID-Chile).

RESULTS:
29.3% of participants presented high multimorbidity, with a significantly higher prevalence among migrants than locals (58.8% vs. 6.8%; p<0.001). Groups differed in sociodemographic composition and access barriers (p<0.002). No significant within group associations were identified in stratified analyses. In the adjusted model, migration status remained strongly associated with high multimorbidity (OR=20.4; 95%CI:13.4–32.2). Lack of healthcare affiliation increased the probability of high multimorbidity among Chileans (OR=4.47; 95%CI:1.99–9.52) but not among migrants, revealing a significant interaction. Model fit was robust (Hosmer–Lemeshow p=0.34; AUC=0.83; Nagelkerke R²=0.42).

CONCLUSIONS:
High multimorbidity disproportionately affects migrants, with a high OR reflecting association rather than prevalence. The interaction between migration status and healthcare affiliation indicates that access to care does not operate uniformly across populations. Policies must incorporate migration-sensitive strategies to promote equitable prevention and management of chronic conditions.