may lead to consumer illness due to pathogen survival even after recommended cooking procedures, and high prevalence of contamination at lower levels makes illness from undercooking or cross contamination more likely. Thus, the events evaluated in the Slaughter Module greatly influence the outcome of the whole model.

This chapter presents the committee’s review of the Slaughter Module. Five primary subjects are addressed: difficulties of data collection, sources of contamination and cross contamination during slaughter and fabrication, the levels (cell density) and extent of carcass and trim surface-area contamination, the effects of decontamination on pathogen prevalence (especially on pathogen load and surface area contaminated), and terminology. Some additional committee observations and comments are offered in Appendix B, and Appendix D is an independent review prepared by Edmund Crouch on the variables used in this module and their implementation in the spreadsheet environment.

LACK OF DATA AND DIFFICULTIES ASSOCIATED WITH DATA COLLECTION

To those unfamiliar with predictive modeling but with some experience in slaughter operations and microbiology, it may be difficult to understand how modeling could be used to predict contamination levels and the size of surfaces contaminated during slaughter and fabrication operations. The task would seem intractable because of the variability and potential unpredictability of events during those operations. Variability in contamination and cross contamination may originate in such factors as plant size, design, age, equipment, automation, speed of slaughter, and animal holding facilities; geographic location; season of the year; type, lot, and origin of animals; labor shift; and personnel training and turnover. As live animals arrive for slaughter, they may be free of E. coli O157:H7 contamination or be contaminated in their gastrointestinal systems or on their hides. Contamination may be localized or may have spread to larger or multiple locations of the hide; the concentration of cells in contaminated spots or niches may be variable. Hide contamination is unpredictable because it can be the result of fecal shedding by individual animal or of cross contamination on the farm, during transportation, or holding before slaughter, when animals enter the slaughter chain. Cross contamination can affect other animals or the plant environment, which in turn can contaminate animals, carcasses, or meat. Fed steers and heifers from one pen are shipped and slaughtered together; culled animals from different farm environments can be commingled and thereby contaminate one another.

Slaughter presents numerous opportunities for contamination and cross contamination that may vary among plants. As the hide is separated



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