Exposure to Industrial Hog Operations and Gastrointestinal Illness in North Carolina, USA

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BACKGROUND AND AIM: With 9 million hogs, North Carolina (NC) is the second leading hog producer in the United States. Most hogs are housed at concentrated animal feeding operations (CAFOs), where millions of tons of hog waste can pollute the air and water with fecal pathogens that can cause diarrhea, vomiting, and/or nausea (known as acute gastrointestinal illness (AGI)). METHODS: We used NC’s ZIP code-level syndromic surveillance system to calculate rates of AGI emergency department (ED) visits during 2016-2019 and swine permit data to estimate hog exposure. Exposure was estimated as the inverse distances from each hog CAFO to census block centroids, weighting with Gaussian decay and by hogs per CAFO, then aggregated to ZIP codes using population weights. We compared ZIP codes in the upper quartile of hog exposure to those without hog exposure. Using inverse probability of treatment weighting, we created a control with similar demographics to the high hog exposed population and calculated rate ratios (RR) using quasi-Poisson models. We examined effect measure modification of rurality and race using adjusted models. RESULTS:Among the 111 high hog exposed ZIP codes, the median number of hogs per ZIP code was 50,022. In high hog exposed areas compared to areas without hog exposure, we observed a 17% increase in AGI rate (95% CI: 1.08, 1.26) and a 24% increase in rural areas (95% CI: 1.04, 1.48). The association was stronger during the weeks after heavy rain (RR=1.54, 95% CI: 1.25, 1.83). When restricted to rural areas, we found an increased AGI rate among American Indian (RR=5.26, 95% CI: 4.60, 5.91) and Black (RR=1.47, 95% CI: 1.04, 1.89) patients. CONCLUSIONS:Residing near hog CAFOs may increase rates of AGI ED visits. Hog CAFOs are disproportionally built near rural Black and American Indian communities in NC and are associated most strongly with increased AGI in these populations. KEYWORDS: Concentrated animal feeding operation (CAFO), animal production, swine, environmental pollution, gastrointestinal illness, waterborne pathogens