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San Francisco, CA
Dr. Blanc is Professor of Medicine, University of California San Francisco, Division of Occupational and Environmental Medicine.
Correspondence to: Paul Blanc MD, FCCP, 350 Parnassus Ave, Suite 609, San Francisco CA 94117; e-mail: blancp{at}itsa.ucsf.edu
Agricultural workers are a particularly important risk group for work-related respiratory disorders and, at the same time, comprise a population that is notoriously difficult to study effectively. The range of conditions of the lower and upper airways to which farmers are prone includes zoonotic infections, extrinsic alveolitis, irritant inhalant injury, organic dust toxic syndrome, and asthma.1 As Chatzi et al2 show convincingly in the January 2005 issue of CHEST, this list of conditions should not omit allergic rhinitis.
The challenges encountered in studying agricultural cohorts are legion. Because by definition they are rural populations, agricultural workers are remote from most medical research centers. Even within the target geographic area of study interest, potential subjects are typically dispersed and often are difficult to contact. Identifying potential study subjects in a way that systematically reflects the underlying population-at-risk and successfully recruiting such subjects is time-consuming and labor-intensive. Choosing a reasonable referent population to compare with a farming cohort (a population that must also be recruited in parallel) is doubly difficult. On all of these counts, Chatzi et al2 have done an admirable job, allowing their study to make a notable contribution to a growing body of medical literature on occupational airways disease in farmers.
The report is significant for a number of other reasons beyond its methodologic strengths. Despite a substantive number of research publications focusing on the epidemiology of airways diseases among farmers, especially asthma, relatively few studies have actually been performed that concern those farmers who cultivate field or orchard crops in outdoor settings. The excellent studies in the Finnish-language literature on occupational asthma in farmers, for example, have largely been driven by the study of cow handlers.3 Other prominent agricultural groups that have been studied in the past few years include swine-confinement workers,4 grain dust-exposed farmers,5 and cultivators employed in greenhouses.6 The powerful European Community Respiratory Health Survey7 has provided interesting observations on asthma risk across a range of occupations including farmers, but because of its largely urban-based and suburban-based sampling design, there are relatively few agricultural workers in that cohort. The largest population-based study of respiratory disease in agriculture that includes substantive numbers of field and orchard crop workers is the European Farmers’ Project, although three quarters of that group have concomitant exposure to cattle, pigs, sheep, or poultry.8
By focusing on farmers who are cultivating a single crop (eg, grapes, predominantly raised for raisins rather than for winemaking), the investigation of Chatzi et al2 is well-positioned to provide insights derived from a highly specific environment that nonetheless may be generalized to other settings. The principal findings indicate a substantially greater prevalence of rhinitis symptoms and positive skin-prick test reactions to aeroallergens among grape farmers compared to control subjects. This latter finding appeared to be driven by pollen sensitivity, especially to allergens associated with plant species that are common weeds in Mediterranean grape-growing regions, consistent with likely occupationally related exposure. The far lower prevalence of sensitization among inhabitants of the same rural locale studied as referents argues against these pollens as simply being regional aeroallergens with exposure that is unrelated to work practices.
The potential importance of work-related rhinitis tends to be discounted within the discipline of occupational medicine as well as in pulmonary practice more generally.9 This is ill-advised. As this study shows, not only were upper airway symptoms linked to grape farming, but so too were a decrement in airflow and an increase in reversible obstruction. Moreover, asthma was indeed more common among the exposed farmers than the referent population, although the number of observations were too few to achieve statistical significance. Beyond its importance as a potential forme furste of occupational asthma,10 rhinitis in and of itself can have a substantive impact on perceived health status and work productivity, and thus should not be disregarded as a source of morbidity.11
Although some of the oldest references in the history of occupational diseases have been to respiratory conditions among farmers, for too long agricultural workers have been presumed to be relatively free of the adverse health risks borne by classic industrial workers or even by other urban service or administrative employees. In terms of allergic sensitization, this idyllic view has been reinforced by recent findings that farm-reared children may be less likely to become atopic than their urban peers,12 even though this cannot be extrapolated to show protection against adult-onset work-related sensitization in agricultural settings. The work of Chatzi et al2 underscores the need to reevaluate these idyllic presumptions.
References
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