Affiliation: Gillings School of Global Public Health, Department of Epidemiology
North Carolina (NC) is the third most hurricane-prone US state and second leading hog producer. Most NC hogs are housed in concentrated animal feeding operations (CAFOs). Hurricane flooding can inundate hog manure lagoons, transporting potentially pathogenic microorganisms into surface water. Drinking contaminated water can result in diarrhea, vomiting, and/or nausea, known as acute gastrointestinal illness (AGI). To investigate the effects of NC’s costliest recent storms, Hurricanes Matthew (2016) and Florence (2018), we calculated AGI emergency department (ED) visit rates from ZIP code-level surveillance data during 2016-2019. Using controlled interrupted time series, we compared AGI ED rates during the three weeks after each hurricane in ZIP codes with a third or more of their area flooded to the predicted rates had the hurricanes not occurred. We estimated ZIP code-level hog CAFO exposure using swine permit data and inverse distance weighting. Using inverse probability of treatment weighting, we created a control with similar demographics to the high hog exposed population and calculated rate ratios using quasi-Poisson models. We assessed the increase in AGI ED rates during the three weeks after the hurricanes in ZIP codes with flooded CAFOs, with flooding but no CAFOs, and with CAFOs but no flooding. We found hurricane flooding to be associated an 11% increase in AGI ED rate (95% CI: 1.00, 1.23) after the hurricanes. We found high hog exposure to be associated with a higher AGI ED rate than no hog exposure (RR=1.17, 95% CI: 1.08, 1.26) and observed increased AGI ED rates among American Indian and Black patients when restricted to rural areas. ZIP codes with hog CAFOs within the flood extents experienced an increase in AGI ED rates during the weeks after the hurricanes compared to the rates in these areas during comparable non-hurricane periods. Areas with hog CAFOs and hurricane flooding had a higher proportion of people of color and lower median incomes than NC overall. Hurricane flooding and hog CAFO exposure highlight environmental and climate justice issues. Black and American Indian residents may disproportionally suffer from AGI in NC, especially residents who live near hog CAFOs and during periods following hurricane flooding.