Advancing Industrial Livestock Production

Abstract

In this issue of EPIDEMIOLOGY, Schinasi et al make an important addition to the growing literature regarding adverse health effects of community exposures to emissions from animal feeding operations. Several controlled epidemiologic studies have reported increased respiratory and other symptoms among residents living close to animal feeding operations, but this is the first study to measure symptomatic and functional responses to specific, well-recognized environmental exposures arising from the industrial production of swine. Even with a relatively small study population of 101, qualitative but repeated measures of odor, H2S (a characteristic emission that comes from animal feeding operations and no other common rural source), PM10, PM2.5, and endotoxin were related to eye and nasal irritation, respiratory symptoms, difficulty breathing, wheezing, chest tightness, nausea, and declines in forced expiratory volume (FEV1). These findings are highly consistent with well-documented adverse health effects among those who were occupationally exposed to animal feeding operations, as well as with the communitybased studies cited above. This research team from the University of North Carolina joined with the Concerned Citizens of Tillery to conduct a community-driven, participatory, and longitudinal study. Their methodological approach is worthy of replication for a number of reasons. The authors have previously documented the reliability and objectivity of this research project in a population of predominantly black, eastern North Carolina residents in 16 communities and living within 2 miles of 1–16 animal feeding operations. Ironically, the poverty and lack of political capital that ties environmentally exposed populations such as these to their homes and communities not only motivates the exposed population to participate in research, but also limits the outward migration of those with exposure-associated health effects (such as asthma), which has been observed in more prosperous rural communities with animal feeding operations. This tends to reduce the selection bias typically observed in populations exposed to airway irritants. The longitudinal study design, with repeated (hundreds) of well-selected measures of biologically relevant acute responses over a 2-week period, provided robust health outcome data. A common misconception is that clinical diseases are the only valid health outcomes, but clinical endpoints such as doctor-diagnosed asthma or chronic changes in lung function are late manifestations of environmental exposures. Furthermore, these endpoints are highly susceptible to selection bias in dose-response studies of airway irritants. It is instructive to note that the US Supreme Court upheld the Department of Labor Cotton Dust Standard which concluded that “grade 1/2 byssinosis (occasional Monday chest tightness) and associated pulmonary function decrements are significant health effects in themselves and should be prevented in so far as possible.” Episodic dose-related respiratory symptoms and declines in expiratory flow are clearly valid measures in setting public policy.