Cancer mortality in workers employed in cattle, pigs, and sheep slaughtering and processing plants

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Abstract

Objectives

We studied mortality in two separate cohorts of workers in abattoirs (N = 4996) and meat processing plants (N = 3642) belonging to a meatcutters' union, because they were exposed to viruses that cause cancer in food animals, and also to chemical carcinogens at work.

Methods

Standardized mortality ratios (SMRs) and proportional mortality ratios (PMRs) were estimated for each cohort as a whole and in subgroups defined by race and sex, using the US general population mortality rates for comparison. Study subjects were followed up from January 1950 to December 2006, during which time over 60% of them died.

Results

An excess of deaths from cancers of the base of the tongue, esophagus, lung, skin, bone and bladder, lymphoid leukemia, and benign tumors of the thyroid and other endocrine glands, and possibly Hodgkin's disease, was observed in abattoir and meat processing workers. Significantly lower SMRs were recorded for cancer of the thymus, mediastinum, pleura, etc., breast cancer, and non-Hodgkin's lymphoma.

Conclusion

This study confirms the excess occurrence of cancer in workers in abattoirs and meat processing plants, butchers, and meatcutters, previously reported in this cohort and other similar cohorts worldwide. Large nested case–control studies are now needed to examine which specific occupational and non-occupational exposures are responsible for the excess. There is now sufficient evidence for steps to be taken to protect workers from carcinogenic exposures at the workplace. There are also serious implications for the general population which may also be exposed to some of these viruses.

Introduction

Workers in the meat industry include persons who work in abattoirs (slaughterhouses) where cattle, pigs, and sheep are slaughtered for human consumption, and those who work in meat processing plants where no killing is done, but the carcasses of these animals killed elsewhere are brought in for processing (by being cut into special smaller pieces, by being cured, spiced, or cooked into various products, or used to manufacture meat-related products such as meat pies, etc.). In large abattoirs, meat processing is also carried out. These food animals and their raw or inadequately cooked products are naturally infected with viruses that cause cancer in the animals. The viruses include, the bovine leukemia virus (BLV), a retrovirus that causes lymphosarcoma in cattle and sheep (Burny and Mammerickx, 1987); jaagsietke sheep retrovirus (JSRV) that causes adenocarcinoma of the lung in sheep (Palmarini and Fan, 2001); ovine nasal adenocarcinoma virus (ONAV) a retrovirus that causes nasal adenocarcinoma in sheep (Cousens et al., 1999, Cousens et al., 2009); caprine nasal adenocarcinoma virus (CNAV) another retrovirus that causes nasal adenocarcinoma in goats (Ortin et al., 2003); and the bovine papilloma viruses (BPVs) that cause cancer of the alimentary tract, bladder cancer, fibromas, fibrosarcomas, meningiomas and chondromas, and warts, in cattle (Campo, 1987, Lancaster and Olson, 1982). It is not known whether these viral agents cause cancer in humans also.

Workers in these plants have one of the highest human exposures to these viruses, and we therefore reason that if these viruses do cause cancer in humans, this should be readily evident in this highly exposed group. Accordingly, we and others have conducted mortality and cancer incidence studies of butchers and meatcutters, and workers in slaughterhouses and meat processing plants (Besson et al., 2006, Boffetta et al., 2000, Coggon et al., 1989, Coggon and Wield, 1995, Doerken and Rehpenning, 1982, Fox et al., 1982, Fritschi et al., 2003, Griffith, 1982, Guberan et al., 1993, Gustavsson et al., 1987, Johnson et al., 1995a, Lagorio et al., 1995, Lynge et al., 1983, McLean et al., 2004, Milham, 1982, Reif et al., 1989). With the exception of studies by Coggon and Wield, 1995, Milham, 1982, the overwhelming majority of the studies have reported an excess occurrence of various cancers, including cancer of the lung, buccal cavity and pharynx, esophagus, bladder, kidney, bone, stomach, larynx, colon/rectum, and prostate.

We previously studied mortality on two occasions in a cohort of workers employed in abattoirs and meat processing plants where cattle, pigs, or sheep were killed and/or processed. Follow-up was from 1949 to 1980 and 1949 to 1989 (Johnson and Fischman, 1982, Johnson et al., 1986a, Johnson et al., 1986b, Johnson, 1989, Johnson et al., 1995a). An excess of cancers of the lung, buccal cavity and pharynx, esophagus, bladder, kidney, bone, and colon was recorded in the cohort. We describe here a further follow-up of this cohort up to the end of 2006, but this time excluding subjects who worked exclusively in predominantly pork processing plants.

Section snippets

Methods

The cohort was identified from a local meatcutters' union in Baltimore, and consisted of 4996 workers who were employed in plants where cattle, pigs, and sheep were killed or killed and processed (heretofore referred to as abattoirs), and a total of 3642 who worked in processing plants that handled these same animals, but where no killing was performed. Carcasses of animals killed elsewhere several days previously are brought in, to these plants for processing. Workers studied were employed

Results

The number of subjects, deaths, and person-years are given in Table 2. As can be seen, the 8638 workers that comprise the study population contributed a total of 337,854.1 person-years, i.e., each study subject contributed an average of 39.1 person-years of observation, and 62% of them died during the study period. Whites contributed 81.1% of the person-years and non-whites 18.9%; males contributed 74.8% of the person-years and females 25.2%. There were 593 subjects born in 1906 or earlier, who

Discussion

Other than race, there were few missing data (Table 1). The findings of this study are important because 1) the average follow-up for study subjects was 39 years (Table 2), which is adequate for investigating diseases with long latency period such as cancers; 2) more than 60% of the workers studied were deceased, which should give a good and fairly representative pattern of mortality in this occupational group; 3) the union records from which the study population was derived were exceptionally

Acknowledgments

This study was funded by a grant (1 RO1 OH008687) from the National Institute for Occupational Safety & Health. Initial funding was provided by the National Institute of Environmental Health Sciences, and the National Cancer Institute. Other than in providing the funds, these agencies had no involvement in the design, collection, analysis, and interpretation of the data. There are no competing interests.

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