Environmental and occupational medicine, 4th edition. Rom WN, Markowitz SB, eds. Philadelphia, PA: Lippincott Williams & Wilkins, 2006 Dec; :570-581
The practice of agriculture has changed substantially over the past 4 decades in response to economic, technologic, and societal factors. Consequently, the agricuitural worker faces a new set of health risks in today's agricultural environment. In the United States during the latter part of the 20th century, there was a shift from the historical pattern of a large number of traditional family-owned and -operated farms to the current condition, in which there are fewer but larger farms that rely on workers who most often do not live on the farm, including seasonal and migrant workers. In the United States, apart from seasonal and migrant workers, between 2 million and 3.5 million individuals work in farming. However, in developing countries, the numbers are much higher in both absolute terms and as a percentage of the population. In Asia, 50% to 70% of the workforce is directly involved in agriculture, and in Africa it is 70% to 90%; thus, farming is the most common industry worldwide. On the 2.1 million farms in the United States there are approximately 700,000 animal confinement workers, including 80,000 poultry farm workers. Changes in the business of agriculture and the agricultural infrastructure have led to the practice of housing large numbers of animals inside buildings, often referred to as concentrated animal feeding operations (CAFOs). This has in turn led to a decrease in the number of swine farms in the United States; in the 1960s, there were over 1.1 million swine farms, but by 1999, there were only about 100,000 (5). Interestingly, the total number of swine raised on these farms has remained stable or increased, accounted for by increasingly concentrated animal populations: there were about 61 million swine in 1915 and 59 million in 2000 (5). In fact, from 1993 to 1999, the number of swine increased by 250%. In CAFOs, animals are kept in enclosed buildings where the air becomes filled with animal-related debris and dust. The increased use of CAFOs has created a variety of new potential health problems, many of which are related to inhalation of animal and other organic dusts. The inhalational health effects of exposure to the agricultural environment are related to several factors: dusts, animal secretions, skin, and feces, as well as bacteria and fungi and their products, including endotoxin. Even though there are fewer farms overall, the Occupational Safety and Health Administration (OSHA) only in frequently evaluates larger operations, and it exempts agricultural operations with ten or fewer employees. As a group, farm workers are the second most likely among all occupations to have never smoked; only members of the clergy are more likely to have never smoked. Epidemiologic studies have shown farmers and other agricultural workers, and perhaps those merely living near agricultural lands and facilities, to be at increased risk of developing lung disease. The increase may be threefold relative to non-fanm workers and is independent of smoking. Agricultural workers ate exposed to a variety of both plant- and animal-derived dusts in the fields and farmyards; they may even inadvertently expose their family members through transfer of dusts into the house via contaminated clothing. This chapter will examine the airway diseases as well as the lung parenchymal diseases commonly associated with agricultural dust exposure.