Date of Award

5-1-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

School of Public Health

First Advisor

Martha J. Felini

Abstract

Objectives: Previous occupational cohort studies among poultry workers have revealed an excess risk of cancer-related mortality, including deaths due to hematopoietic malignancies. However, specific occupational and non-occupational exposures contributing to this excess risk have yet to be identified. Poultry workers are particularly at high risk since an average of 175,000 chickens are killed daily in poultry plants in the United States. This brings poultry workers into intimate contact with their blood, organs, and secretions, which may harbor transmissible oncogenic viruses. Moreover, they are exposed to potentially carcinogenic chemicals that are emitted during packaging and preparation. Hence, our study was conducted to provide preliminary evidence of which specific poultry related and non-poultry related occupational tasks increase the risk of mortality from hematopoietic cancer among poultry workers. Methods: A pilot case-cohort study was conducted using a combined cohort of 30,411 highly exposed poultry workers and 16,408 control subjects. Exposures pertaining to poultry and non-poultry related tasks were self-reported through telephone interviews from controls and next-of-kin for cases. Hematopoietic cancer mortality risk was assessed using logistic regression odds ratios (OR) and proportional hazard ratios (HR). Results: To assess possible differential recall between responses obtained directly from live study subjects and those from the next-of kin of deceased study subjects, the questionnaire was administered to a small subset of seven pairs of live control study subjects and their next-of-kin. Of the 245 direct responses obtained for dichotomous questions, there was an agreement of 80 % to 100% between the pairs for nearly 75% of the responses, with less than 60% agreement for only 8% of the responses. The highest risks for hematopoietic cancer mortality were among poultry workers in stockyards (OR=4.50, 95%CI=0.34-59.88), work as a poultry farmer (OR=2.67, 95%CI=0.78-9.23), working in non-commercial poultry farms (OR=2.53, 95%CI=0.85-7.52), handling of raw eggs in grocery stores (OR= 2.24, 95%CI=0.05-9.78), working in commercial poultry farms (OR=2.41, 95%CI=0.79-7.33), and spreading of chicken wastes (OR=2.00, 95%CI=0.58-6.89). Direct contact with poultry blood (OR=1.40, 95%CI=0.66-2.95) and killing chickens at work or outside of work (OR=1.35, 95%CI=0.26-7.14 and 1.63 (95%CI=0.72-3.65, respectively) were exposures that were also associated with an increased risk. Among non-poultry associated occupational exposures, working in a chemical plant (OR=6.92, 95%CI=0.56-85.23) and spraying insecticides (OR=3.03, 95%CI=0.78-11.83) incurred an increased risk. Work-related exposure to coal tar, naphthalene, or paraffin was associated with a significantly increased risk (OR=5.63, 95%CI=1.72-18.43). An elevated risk was also observed among subjects that worked at a gasoline station (OR=1.89, 95%CI=0.52-6.96). These exposures are known to be associated with increased exposures to PAHs and benzene. There was a statistically significant increased risk among those who sold seafood at work (OR=4.31, 95%CI=1.08-17.16) and among participants who worked on a commercial mixed farm (OR=3.15, 95%CI=1.20-9.92). Conclusion: This study provides preliminary evidence that exposure to poultry may be associated with increased mortality from hematopoietic cancer. A plausible explanation is that stockyard workers are regularly exposed to the bodily fluids of poultry, including blood and fecal matter, which may harbor oncogenic viruses that are transmissible to humans. The elevated risk estimates among workers exposed to gasoline as well as chemicals such as coal tar corroborate findings from previous studies that have established benzene and PAHs as risk factors for hematopoietic malignancies, respectively. While our findings support evidence from previous studies linking pesticide use and working on farms with mortality due to hematopoietic cancer, selling seafood was a unique risk factor that was discovered in our study, worthy of further investigation. Case-control studies nested within occupational cohorts of highly exposed subjects of sufficient statistical power may provide an efficient and valid method of investigating and confirming these findings.