When it Comes to COVID-19 Outcome, ZIP Code Matters

COVID-19 patients’ ZIP codes influenced how sick they were upon hospitalization, and how much care they needed after admittance.

One study, published today in Annals of Internal Medicine, looked for a linkage between COVID-19 hospitalization outcomes and neighborhood-level social vulnerability. The study authors had previously found US counties with elevated levels of social vulnerability or disadvantage experience greater COVID-19 infection, morbidity, and mortality.

The investigators measured social vulnerability using the social vulnerability index (SVI), a composite measurement of social disadvantage. The SVI was developed by the US Centers for Disease Control and Prevention (CDC) to provide an aggregate measure of the various neighborhood factors known to influence disease outbreaks and other public health crises. The SVI included 4 subindices: socioeconomic status, racial/ethnic minority status and language, housing type and transportation, and household composition and disability.

This study used data from a cohort of 38 Michigan hospitals and ZIP code-linked SVI to quantify the individual- and neighborhood-level factors that influence COVID-19 hospitalization outcomes.

The monitored COVID-19 infection outcomes included acute organ disfunction, organ failure, invasive mechanical ventilation, intensive care unit stay, death, and discharge disposition.

After recruiting 2678 patients 18 and older hospitalized with COVID-19 from March-December 2020, the investigators performed pooled cross-sectional analysis. They merged clinical data pulled from patient charts with the SVI to understand how COVID-19 outcomes differed by ZIP code.

At the time of hospital admission, patients living in high-vulnerability ZIP codes had lower pulse oximetry readings and higher respiratory rates than patients from low-vulnerability ZIP codes.

Once admitted, the hospital patients in high-vulnerability ZIP codes required intensive care unit treatment more frequently (29.0%) than patients in low-vulnerability ZIP codes (24.5%). In comparison to those from low-vulnerability ZIP codes, patients from high-vulnerability were also more likely to receive a mechanical ventilator (19.3% vs. 14.2%), as well as experience higher rates of organ dysfunction (51.9% vs. 48.6%), organ failure (54.7% vs. 51.6%), and in-hospital death (19.4% vs. 16.7%).

These results remained robust even after the investigators adjusted for individual-level factors, such as patient age or comorbid conditions. Notably, however, after the patients were admitted and treated, there were no differences in hospital mortality of discharge disposition. This suggests neighborhood social disadvantage operates independently of patient clinical characteristics and hospital treatment.

The study authors surmised, "Hospitalized patients with COVID-19 from socially vulnerable neighborhoods presented with greater illness severity and required more intensive treatment, but once hospitalized they did not experience differences in hospital mortality or discharge disposition."

The investigators hope the results of this study will enable politicians to provide high-vulnerability ZIP codes with more resources and access to COVID-19 services. They specifically recommended increased COVID-19 testing, treatment, and vaccination for socially vulnerable ZIP codes.