From the Journals

Income inequality plus race drive COVID incidence, death rates in U.S.



Income inequality corresponds to higher COVID-19 incidence and mortality beyond the effects of race and ethnicity, according to an analysis of U.S. county-level data.

Transmission electron micrograph of SARS-CoV-2 virus particles Courtesy NIAID

The study, published in JAMA Network Open (2021 Jan 20. doi: 10.1001/jamanetworkopen.2020.34578), was led by Tim F. Liao, PhD, of the University of Illinois at Urbana-Champaign, and Fernando de Maio, of DePaul University, Chicago. They wrote: “This analysis confirms the association between racial/ethnic composition and COVID-19 incidence and mortality. A higher level of Black or Hispanic composition in a county is associated with a higher COVID-19 incidence and mortality; a higher level of economic inequality is also associated with a higher level of incidence and mortality.”

The analysis, which examined data from the first 200 days of the pandemic from January to August 2020, examined the joint associations between income inequality and racial and ethnic composition. Researchers mined data from the Centers for Disease Control and Prevention, the Census Bureau, the Kaiser Family Foundation, and other sources for 3,142 U.S. counties.

Income inequality was measured with the Gini index, on a 0-100 scale, with zero meaning perfect income equality (everyone has the same income) and 100 meaning perfect inequality (only one person or group has all of the income). The average Gini score across all the counties was 44.5, with a range of 25.6-66.5.

Researchers found that, for every 1.0% increase in a county’s Black population, there was a 1.9% increase in COVID-19 incidence (risk ratio, 1.019; 95% confidence interval, 1.016-1.022) and a 2.6% increase in COVID-19 mortality (RR, 1.026; 95% CI, 1.020-1.033). For every 1.0% increase in a county’s Hispanic population, there was a 2.4% increase in incidence (RR, 1.024; 95% CI, 1.012-1.025) and a 1.9% increase in mortality (RR, 1.019; 95% CI, 1.012-1.025).

Income inequality had an even greater effect on COVID-19 incidence and mortality. For each 1.0% rise in a county’s income inequality, there was a 2.0% rise in incidence (RR, 1.020; 95% CI, 1.012-1.027), and a 3.0% rise in mortality (RR, 1.030; 95% CI, 1.012-1.047).

In counties with lower percentages of Black and Hispanic population – up to about 50% for blacks and about 20%-30% for Hispanics – greater income inequality was correlated with higher COVID-19 incidence and mortality. But as the proportion of the Black and Hispanic population increased, race and ethnic population became the much more dominant predictive factor. In other words, the researchers said, income inequality seems to become less of a factor in COVID-related health as the minority population number grows in a given county.

“This finding implies that counties with relatively low proportions of Black or Hispanic residents may experience health effects of income inequality associated with the neomaterial pathway, which connects income inequality to population health through the breakdown of public infrastructure,” such as education, transportation and health care, the researchers said.

The study also examined the interaction between these factors and political attributes of a county, such as whether a governor faced a term limit, was Republican, or was male, and these were found to have no effect on COVID-19 incidence and mortality. Counties in states participating in Medicaid expansion under the Affordable Care Act had a 32% lower COVID-19 incidence rate, researchers found, but there was no correlation with mortality rates.

“This analysis found racial/ethnic composition, while important, does not reveal the full complexity of the story,” the researchers wrote. “Income inequality – a measure not typically included in public health county-level surveillance – also needs to be considered as a driver of the disproportionate burden borne by minoritized communities across the United States.”

The findings, they said, support using composite variables that “measure both income inequality and racial/ethnic composition simultaneously.”

The investigators had no disclosures.

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