Asthma-like diseases in agriculture

Abstract

Although many studies on asthma have been conducted in farming populations, no longitudinal studies have been published so far. Smoking, work in pig barns, and crop farming together with exposure to endotoxin and quaternary ammonium have been described as environmental risk factors for self-reported asthma and/or wheeze in cross-sectional studies. The prevalence of self-reported asthma has been found to range from 0.7% in female greenhouse workers to 21% in Danish smoking female farming students. Exposure in farming is diverse, but dominated by organic dust containing high amounts of compounds known to trigger the innate immune system. This is confirmed by a wide range of human experimentation where nave persons have been introduced to swine confinements. Cross-sectional data suggest a protective effect of farming on allergy. However, differences in the diagnostic procedure and the predominantly wheezy asthma type in farming concomitant with a lower rate of allergic asthma makes the comparison difficult. Furthermore, healthy worker selection, misclassification, age differences, difference in time of study and small study populations, resulting in low statistical power, might be factors explaining the findings. Well-designed longitudinal studies of the incidence of carefully defined phenotypes of asthma and risk factors are needed to clarify the risk of asthma, or wheezy phenotypes related to farming.