Cohort studies in farmers or agricultural workers have mostly been targeted at cancer outcomes; those focused on other health issues are scarce. The overall findings suggest that farmers and farm residents experience less cancer and more favorable mortality patterns, except from accidents, than their respective control groups. Liver cirrhosis as a cause of death was significantly less than expected in New York farmers, and so was the incidence of liver and kidney cancer in several cohorts of farmers, agricultural workers, and licensed pesticides applicators in other studies (3-7).
One cohort study among farmers and agricultural workers from Italy found a small excess of kidney cancers based on five observations against the background of overall reduced cancer mortality. Studies in female farm residents have shown either insignificant elevations of liver cancer risk or no elevations at all, with kidney cancer risk being significantly reduced. In a large case-control study of hepatocellular carcinoma, cholangiocarcinoma, or combined hepatocellular and cholangiocarcinoma, male farmers were the only occupational group with an odds ratio significantly below unity. A few studies suggest that migrant farm workers may differ from farmers by experiencing excesses of cancers of the buccal cavity and pharynx, lung, and liver. This disease pattern, however, appears to be more closely related to lifestyle factors like smoking and alcohol drinking than to occupational exposures typically associated with farming (8-13).
Only few reports describe relevant disease patterns deviating from the above-mentioned findings. One was a cluster of 14 hepatic angiosarcoma cases in Egypt, 10 of which had "a definite history of a direct chronic recurrent exposure to agricultural pesticides of variable chemical nature." The authors' conclusion that "this significant increase .. . among farmers involved in pesticide spraying suggests that agricultural pesticides might play a role in the genesis of hepatic angiosarcoma" does not hold, however, against the lack of evidence in the rest of the available literature (14).
Elevated rates of liver cancer in rural populations in Fiji as compared to Tonga have been attributed to the higher prevalence of food contamination with aflatoxin in the former, reflecting different storage practices. Men who used mainly dichlorodiphenyl-trichloroethane (DDT) in an antimalarial campaign in Sardinia, Italy, during the late 1940s experienced an increased mortality from liver and biliary tract cancers. This increase, however, also occurred in nonexposed subjects and showed no dose response relation. The authors concluded that these cancers probably were unrelated to DDT and that other environmental exposures common to the Sardinian population accounted for the increase in risk (15,16).
In a report on a case series on end-stage renal disease (ESRD) in El Salvador, the authors described a group of patients with known risk factors for ESRD, basically diabetes mellitus, hypertension, and chronic consumption of nonsteroidal antiinflammatories. Another group had unusual characteristics that were not associated with the known risk factors. According to the authors they "identified an important group of patients with ESRD who seem to lack a cause for their disease. Their special characteristics make it possible to suspect a relationship with the occupational exposure to insecticides or pesticides." While this interpretation contrasts with the lack of similar findings in other rural populations from other regions, it is a perfect illustration of a widespread perception bias in parts of the epidemiological literature on health risks associated with agriculture: health effects are readily attributed to agricultural chemicals, notably pesticides, without even trying to define what pesticides are, and without adequate consideration of other possible causes (17).
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