California Healthy Places Index and COVID-19 hospitalization risk: a patient-level analysis

Research has shown that inequalities in COVID-19 outcomes are influenced by individual-level characteristics and specific measures of neighborhood characteristics. Understanding the association between composite neighborhood-level social determinants of health, particularly newly developed determinant indices, and COVID-19 outcomes is important. The objective of this study is to contribute to the literature by evaluating the association between the California Healthy Places Index (HPI)-an extensive yet relatively underutilized measure of neighborhood health and well-being-and a significant health outcome at the patient level, hospitalization related to COVID-19.

Utilizing a retrospective cohort study design, we examined electronic health record data from adult patients who tested positive for COVID-19 between 2/1/2020 and 2/3/2022 at an academic medical center in Northern California. The primary outcome was hospitalization within 14 days of the first COVID-19 diagnosis. We used both unadjusted and multivariable logistic generalized linear mixed models with random intercepts at the county and ZIP code (nested within county) levels to examine the relationship between California HPI quartiles-where the lowest quartile represents the most disadvantaged neighborhoods-and COVID-19 hospitalization. The multivariable model adjusted for individual-level characteristics as covariates.

Of the 21,831 patients included in the cohort, 1,355 (6.2%) were hospitalized with COVID-19. The results demonstrated a dose-response relationship between the California Healthy Places Index (HPI) and patient-level COVID-19 hospitalization in the unadjusted model, and this association remained significant after adjusting for covariates. In the multivariable model, patients living in neighborhoods within the lowest HPI quartile had the highest odds of hospitalization (adjusted odds ratio [AOR] = 1.90, 95% confidence interval [CI] = 1.28-2.83; average marginal effect [AME] = 0.04, 95% CI = 0.01-0.06) compared to those in the highest quartile, followed by patients in the second and third quartiles.

Study findings indicate that among patients with COVID-19, residence in more disadvantaged neighborhoods was associated with higher hospitalization rates. These results could encourage investigation into neighborhood-level social determinants of health, such as those measured by the California HPI, and their associations with health inequities. They may also inform future research exploring causal mechanisms underlying these inequities and could guide evaluation of targeted interventions to address them.