School proximity to concentrated animal feeding operations and prevalence of asthma in students

Asthma prevalence and severity are rising in industrialized nations. Studies supporting the hygiene hypothesis suggest that being raised on a farm protects against atopy and, often, asthma. In rural United States, however, an increased rate of asthma has been found among schoolchildren. We hypothesized that the rural US environment may not be protective against airway inflammation, perhaps due to environmental effluents from a relatively high number of concentrated animal feeding operations (CAFOs). We compared the prevalence of asthma in two Iowa elementary schools, one adjacent to a CAFO, and the other distant from any large-scale farming operations.

Cross-sectional questionnaire-based study.

Two rural Iowa elementary schools: the study school is located one-half mile from a CAFO, and the control school is distant from any large-scale agricultural operation.

Children, kindergarten through grade 5, who attended either the study school or the control school.

Children in the study school had a significantly increased prevalence of physician-diagnosed asthma (adjusted odds ratio, 5.71; p = 0.004). Although this group was more likely to live on a farm and have parents who smoke, these potentially confounding variables did not account for increased prevalence in a multivariate model. No difference in measures of asthma severity was found between the two populations. Because different sets of physicians are responsible for the medical care of the groups of children, it is possible that physician bias is responsible for the different prevalence of asthma diagnoses. This was not explored in the study.

This study supports a role for exposure to rural environmental toxicants in the etiology of asthma, and suggests a need for further study of this relationship.