Study links N.C. hog feeding operations to acute gastrointestinal illness

November 23, 2022

Dr. Arbor Quist

North Carolina’s rapidly growing human population of over 10 million puts it ninth on the list of most populous states in the U.S. It may come as a surprise to learn that this number is nearly matched by the number of hogs, which at nine million, makes North Carolina one of the highest hog producers in the country. Industrial agricultural practices that bring thousands of these hogs together in one site have raised serious concerns about health risks they pose to the human residents of North Carolina. A study team led by Arbor Quist, PhD ’21 (epidemiology), a researcher at the Gillings School of Global Public Health, conducted an investigation, with results published earlier this year in Science of The Total Environment, to see how common gastrointestinal illness was among people who live close to these operations.

“Listening to residents talk about how their quality of life and health is affected by living near industrial animal operations led to this study,” said Quist. “Common complaints related to malodors and respiratory issues, and I was interested in how I could use existing data to examine additional health outcomes to further understand and quantify the effects of industrial hog operations on health and environmental injustice.”

Concentrated animal feeding operations (CAFOs) hold at least 1,000 “animal units” (between 2,500 and 10,000 hogs) for at least 45 days, and these facilities house a majority of N.C.’s hogs. Because of their size, CAFOs produce immense quantities of animal waste – more than the human population of the state – and this waste is held in large, uncovered pits or sprayed on open land as fertilizer. Research by the late Dr. Steve Wing, associate professor of epidemiology at the Gillings School, in the wake of Hurricane Floyd showed significant environmental and health risk posed by this waste and noted elevated rates of health issues in nearby communities, including irritation of the nose, throat and eyes; diarrhea; treatment-resistant bacterial infection; and elevated risk of cardiovascular mortality.

Hog waste is known to contain pathogens responsible for acute gastrointestinal illness in humans, which can cause vomiting, diarrhea and nausea, and this new study builds on Wing’s pioneering work by examining the frequency of this type of illness in communities near CAFOs, comparing them with similar communities that are not situated near highly concentrated animal populations.

To identify potential health impacts, the research team examined data about emergency department visits for acute gastrointestinal illness based on zip code of residence. To estimate hog exposure, the team used permitting data to determine the location and size of CAFOs, and weighted residents’ exposure based on their distance from and the amount of manure present at the nearby operation.

“Poultry CAFOs and hog CAFOs are often co-located in eastern N.C., making it difficult to isolate the effect of hog CAFOs,” said Quist. “In an attempt to address this, we conducted sensitivity analyses where ZIP codes with any poultry CAFOs within five miles were excluded from the control group. We also examined the association between exposure to both poultry and hog CAFOs, where we found an even stronger association with rates of emergency department visits for acute gastrointestinal illness.”

David Richardson

Dr. Lawrence S. Engel

The team found that living near CAFOs may increase risk of acute gastrointestinal disease to a significant degree, and this effect varied by the area’s “rurality” — a classification based on the accessibility of resources. Further, in rural areas, the prevalence of gastrointestinal illness was significantly higher among American Indian and Black residents. The team also noted elevated occurrence of disease immediately following periods of heavy rain and in areas with both poultry and hog CAFOs.

Compared to the control population, which was not exposed to CAFOs, the study team found that areas with high hog exposure were associated with an 11% increase in emergency department visits for acute gastrointestinal illness. For rural areas, which are more likely to rely on well water, cases of disease were 21% higher.

To a disproportionate degree, these CAFOs are built near Black and American Indian communities in N.C., and members of these communities have higher rates of disease.

Cumulative research into the effects that this relatively new type of agriculture has on nearby populations is uncovering concerning effects on health and the environment.

“These results provide additional evidence of the adverse health effects associated with industrial hog operations that disproportionately harm people of color in North Carolina,” said Quist. “The results also suggest that removing industrial hog operations from heavy rain-prone areas may reduce rates of gastrointestinal illness. Our next paper will examine the combined effect of hurricanes and industrial hog operations on gastrointestinal illness in North Carolina.”

The study team included Mike Dolan Fliss, PhD, MPS, MSW, research scientist at the Injury Prevention Research Center, housed at the Gillings School; Paul L. Delamater, PhD, assistant professor in UNC’s Department of Geography; and three of Quist’s colleagues from the Department of Epidemiology: David A. Holcomb, PhD, postdoctoral researcher, David Richardson, PhD, associate professor, and Lawrence S. Engel, PhD, associate professor.

Contact the UNC Gillings School of Global Public Health communications team at sphcomm@unc.edu.