BACKGROUND:

In 1986 when the study began, agriculture was one of the largest employers in the United States, comprising nearly 12 million people. Farm workers were hospitalized more frequently than other occupational groups and were found to have the highest number of restricted activity days due to injury and illness. Much of this was due to frequent and disabling farm related accidents which made agriculture the most hazardous occupation in the United States. Agricultural workers were also found to have high rates of respiratory disability, compared with other industrial sectors, based on Social Security disability records.

The common denominator for respiratory disorders among agricultural workers was exposure to organic dust which was recognized to be a complex mixture of vegetable particles and fragments, microorganisms and their products, insects and insect fragments, feed additives including fish meal and antibiotics, and avian and rodent proteins. While the vegetable dust itself was by far the most important exposure, individual circumstances of growing, storage and subsequent use of the product from which the organic dust arose, influenced specific exposures. In certain situations, like animal confinement housing, irritant gases including ammonia and hydrogen sulfide co-existed with an organic dust to further vary respiratory exposure.

Workers exposed in Iowa swine production units were known to be significantly exposed to grain dust, endotoxin, animal danders and other proteins, ammonia and hydrogen sulfide gas, and a variety of microorganisms including fungi and thermophilic actinomycetes. Cross-sectional epidemiological surveys had documented a high prevalence of respiratory symptoms including chronic cough, phlegm and wheezing, but also prominent constitutional symptoms including fever, myalgias and malaise. This study was one of several projects supported by a Specialized Center of Research in Occupational and Immunologic Lung Disease.

Funding represents approximately 35 percent of the dollars of the Specialized Center of Research in Occupational and Immunologic Lung Disease (P50HL37121) used to support epidemiologic studies.

DESIGN NARRATIVE:

A nested case-control study was carried out on a previously studied cohort. Members of the cohort were resurveyed in the first year of the study. All participants received a routine physical examination, chest x-ray, electrocardiogram if over 40 years of age, routine laboratory tests, methacholine challenge, intradermal skin testing, and bronchoalveolar lavage. Cases for the swine confinement farmer cohort were selected if they had FEF50 of 60 percent or less of predicted for age, sex, height, and race. Three referents for each case were randomly selected from all swine confinement farmers not selected as cases, non-confinement farmers, and blue collar workers. Measurements were repeated in the fourth year, finishing in the fifth year of the study. The study determined: the extent to which epidemiological studies underestimated pulmonary responses and impairments among agricultural workers; the environmental risk factors significantly related to cases; whether atopy and heightened airway reactivity were significantly associated risk factors. The subproject was not renewed in 1992.