Respiratory health effects in pig farmers : assessment of exposure and epidemiological studies of risk factors

This thesis describes a cross-sectional study of risk factors of chronic respiratory health effects in pig farmers working in the South of the Netherlands. The study population comprised 100 pig farmers with and 100 pig farmers without chronic respiratory symptoms. Base-line lung function, non-specific bronchial responsiveness, and specific antibodies to common and work- related antigens were determined as well. Exposure to dust, endotoxins and ammonia was measured by personal sampling during two days. Exposure to disinfectants was characterized by the type of disinfectant and procedure features. As part of the study, long-term average exposure to endotoxins was modelled using information on task activity patterns during two weeks and on farm characteristics; exposure-response relationships would be seriously underestimated if measured exposure would be used due to the large day-to-day variability relative to variation between individuals. Results of this epidemiological study suggest that the etiology of respiratory health effects in pig farmers is complex, involving different exposures and several mechanisms. The strongest evidence for a potential causal role of exposure was found for disinfectants and endotoxins, which may act either independently of atopy, or interact with atopic (IgE) sensitization to common allergens. It seems likely that IgE sensitization to common allergens can be induced by the use of disinfectants, specifically by those containing quaternary ammonium compounds. IgG 4 antibodies against work-related antigens were inversely related to respiratory impairment, potentially reflecting a protective effect of this type of antibodies. Change of disinfection procedures, application of specific farm characteristics, and the use of personal protective equipment can be considered as control measures to reduce health hazards, but additional studies are required to estimate the actual effect. Future epidemiological studies could provide evidence on the etiology of respiratory health effects when sufficient subjects are being studied in prospective studies and different etiological pathways are being considered. The exposure should be assessed on multiple occasions.