Factors Associated with Readmission Risk in Patients with HIV Stratified by BMI: A Hospital-Based Retrospective Matched Cohort Study

Background : The role of body mass index (BMI) as an effect modifier for readmission risk in people with HIV (PWH) remains underexplored. Objective: To compare factors associated with two-year all-cause readmission in PWH, stratified by baseline BMI. Methods: A retrospective matched (1:1 by age/sex) cohort study was conducted at a major public infectious diseases hospital in Shenzhen, China, serving a diverse urban population including migrants and low-income individuals. Adults admitted (Jan-Jun 2020) were stratified into underweight (BMI<18.5 kg/m², n=80) and normal/overweight (BMI 18.5-<28 kg/m², n=231) groups. Multivariable logistic regression and ROC analysis were performed within each stratum. Results: The readmission rate was higher in the underweight group (61.3% vs. 46.8%, p=0.023). For underweight PWH, unemployment (adjusted Odds Ratio [aOR]=8.11, 95% CI: 1.82-36.16) and lower nadir CD4+ count (aOR=0.994 per cell/μL decrease, 95% CI: 0.989-0.999) were independent risk factors. For normal/overweight PWH, unemployment (aOR=2.21, 95% CI: 1.12-4.38) and longer time since diagnosis (>5 vs. 0-1 years, aOR=4.28, 95% CI: 2.02-9.07) were risk factors, while being widowed/divorced was protective (aOR=0.30, 95% CI: 0.10-0.86). Predictive models showed good to excellent accuracy (AUCs: 0.820 and 0.748, respectively). Conclusions: Risk factors for readmission differ markedly by baseline BMI, confirming its role as an effect modifier. Interventions should be tailored: integrated nutritional and immunological support for underweight PWH, and chronic disease management with attention to social determinants for others.