An Ecologic Study of Disparities in COVID-19 Incidence and Case Fatality in Oakland County, MI, USA, During a State-Mandated Shutdown.

INTRODUCTION: Data from the USA reveal disparities in hospitalization and mortality from coronavirus disease 2019 (COVID-19). Social determinants of health (SDoH) could account for disparities in disease incidence and outcomes. We investigated the association between zip code racial composition and COVID-19 incidence and case fatality in Oakland County, MI. METHODS: We conducted an ecological study using publicly available data on COVID-19 in 70 zip codes in Oakland County, MI. We obtained demographic surrogate markers of SDoH by zip code from the US Census Bureau website. Using negative binomial regression models, we investigated the association between the percentage of Blacks in each zip code and COVID-19 incidence and case fatality, including markers of SDoH as potential confounders. RESULTS: Reported COVID-19 cases ranged from 13.2 to 255.2 per 10,000 population. Each percentage increase in Blacks within a zip code was associated with a 3% increase in COVID-19 cases (95% CI: 1.02 to 1.04, p ≤ 0.0001), and this remained significant after adjusting for income or poverty level, number of persons per household, mode of transportation, age, and level of education (incidence rate ratio: 1.02, 95% CI: 1.01 to 1.03, p ≤ 0.0001). Zip codes with a higher percentage of Blacks also experienced a faster increase in COVID-19 rates from April 3 to May 16. However, the proportion of Blacks in a zip code was not associated with case fatality. CONCLUSION: Zip codes with larger Black populations were disproportionately affected by COVID-19.