Escherichia coli O157:H7 in Ground Beef Review of a Draft Risk Assessment (2002) / Chapter Skim
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3 Slaughter Module
3 Slaughter Module
Pages 41-61
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From page 41... ...
The Slaughter Module bridges the two, examining the factors that affect the amount of fecal and hide contamination that is introduced into and remains on carcasses and how this contamination is distributed on the meat cuts and trimmings that become ground beef. The extent and level of contamination in turn influence the efficacy of cooking in eliminating pathogens from the readyto-eat product and thus human exposure.
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From page 42... ...
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.
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From page 43... ...
Available data exist only to support the suggestion that dehiding results in carcass contamination (in terms of prevalence) and that decontamination interventions can have a substantial effect in reducing prevalence and levels of contamination if applied properly.
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From page 44... ...
However, the lack of publicly available data on crucial steps in the slaughter process, the variability of the operations modeled in the module, and the potential unpredictability of the effects of some activities on contamination during slaughter and fabrication complicate modeling and limit its ability to predict outcomes. The committee recommends that the impact of data deficiencies and difficulties associated with data collection, which have been recognized in various parts of the FSIS draft risk assessment document, be more strongly emphasized in discussions of the outcomes calculated by the model.
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From page 45... ...
The FSIS draft risk assessment acknowledges that cross contamination may occur and notes that the hide is an additional source of contamination. The draft's justifications for using fecal contamination as the only source of carcass contamination are in the discussion of the knock box and stunning operations: there are sparse data on hide prevalence, the contribution of hide contamination is implicit in the existing model, and research indicates that the fecal status of incoming cattle correlates most strongly with carcass contamination.
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From page 46... ...
Those observations confirm that contamination originates in feces and hides as well as from cross contamination (even if animal testing yields zero prevalence) ; hide removal is the most important operation that results in exposure of carcasses to contamination; slaughter-plant operations after dehiding, including decontamination processes, reduce contamination greatly, in terms of both lot and sample prevalence; and carcass contamination before evisceration, after evisceration, and especially after processing does not correlate well with fecal or hide contamination.
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From page 47... ...
The Effect of Slaughter-Plant Methods on Cross Contamination of Carcasses The FSIS draft risk assessment states that cross contamination of hides may occur in the knock box as noncontaminated cattle fall to the floor or come into contact with sides of the chute after contaminated cattle have passed through. It also cites literature that finds that additional contamination can occur if cattle emit feces or rumen contents at the knock box or if dirty knives are used.
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From page 48... ...
It notes that "the overall prevalence of carcass contamination with EHEC 0157 was significantly greater than that of fecal and hide prevalence" and that carcass samples in the same lot were positive even when no animals were fecal- or hide-positive. And the FSIS draft risk assessment recognizes the importance of self-contamination and
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From page 49... ...
Issues Regarding the Accuracy with Which Data Were Copied from Sources A transformation ratio (TR) is used in the FSIS draft risk assessment to relate the frequency of contaminated carcasses to the frequency of cattle in a lot carrying the pathogen.
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From page 50... ...
The committee recommends that the numbers found in the FSIS draft risk assessment and attendant model be cross-checked for accuracy with the data presented in the published study of Elder et al.
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From page 51... ...
The FSIS draft authors manage it by subjectively setting the minimum area of contamination at 30 cm2 and the maximum area at 3,000 cm2 because "initial model runs showed that contaminated surface areas greater than 3,000 cm2 produced results that were infeasible in comparison with FSIS ground beef sampling data." The range of contamination density predicted with those assumptions is 1 to 9,000 cells. The committee acknowledges that such data are difficult to obtain or predict and that contamination of the carcass surface is expected to be localized, nonuniform, random, and nonhomogeneous, and notes that the range of contamination density predicted may well be wide enough to account for all the unknowns in the calculation.
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From page 52... ...
First Decontamination The committee notes that not all plants apply a first decontamination; this should be explicitly recognized in the risk assessment. The FSIS draft notes that a variety of organic acids are used for decontamination, but it does not specify which, if any, are in common use.
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From page 53... ...
· The procedures used for the second decontamination depend not only on the size of the plant, as stated in the draft risk assessment, but also on such factors as equipment availability, costs, plant design, space available, and steam availability. · All plants use knife trimming and some type of water rinsing or spraying, but steam pasteurization is not used universally (although it is quite common)
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From page 54... ...
. was modeled using triangular distribution with a minimum value of O logs, an uncertain most-likely value of 0.5 to 1.5 logs, and an uncertain maximum value of 1.51 to 2.5 logs." Those values appear reasonable, but the committee recommends that the risk assessment explicitly state the reasoning underlying them and note, if appropriate, that they apply not only to steam pasteurization but also to other methods applied individually or in combination in carcass decontamination.
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From page 55... ...
TERMINOLOGY CONCERNS As noted elsewhere in this review, the FSIS draft risk assessment sometimes defines or uses terms in nonstandard ways. The committee found a few circumstances in the Slaughter Module in which that might confuse readers.
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From page 56... ...
also addresses this point. OTHER OBSERVATIONS The FSIS draft risk assessment models cows and bulls separately from steers and heifers because most operations slaughter one of the two groups of animals.
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From page 57... ...
Furthermore, although the FSIS draft risk assessment states that those values represent midpoints of uncertainty distributions that "can range +20%" (p.
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From page 58... ...
However, the lack of publicly available data on crucial steps in the slaughter process, the variability of the operations modeled in the Slaughter Module, and the potential unpredictability of the effects of some activities on contamination during slaughter and carcass fabrication complicate modeling and limit the module's predictive capacity. The lack of data has made development of the model difficult and has created the necessity to rely heavily on the results of one study (Elder et al., 2000)
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From page 59... ...
1997. Effects of acetic acid, lactic acid and trisodium phosphate on the microflora of refrigerated beef carcass surface tissue inoculated with Escherichia cold 0157:H7, Listeria innocua, and Clostridium sporogenes.
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2002a. Effect of acid adaptation on survival of Escherichia cold 0157:H7 in meat decontamination washing fluids, and potential effects of organic acid interventions on the microbial ecology of the meat plant environment.
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From page 61... ...
l999c. Extent of beef carcass contamination with Escherichia cold and probabilities of passing U.S.
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