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s
Microbiologic and Toxicologic Assessment
Abstract Microbiologic and toxicologic (chemical) hazards that are vitally
important to public health are not addressed in SIS-C. Continuous assessment of such
hazards based on scientifically valid sampling and the use of more effective methods
must be a part of any meat inspection system. Moreover, research must be conducted
on slaughtered cattle to provide statistically valid data to test hypotheses relating to
microbiologic and toxicologic hazards in order to enhance and preserve public health
and restore public confidence in the current inspection system.
Assessment
As emphasized in previous Food and Nutrition Board (FNB) reports (NRC,
19SSa, 1987a), microbiologic and toxicologic hazards represent the greatest risk to
human health associated with meat. A full assessment of possible microbiologic and
toxicologic risks associated with red meat goes well beyond the charge of this
committee. These risks have been reviewed in detail in previous Food and Nutrition
Board reports (NRC, 19SSa,1987a). Table 5-l is taken from the 19SS report Meat and
Poult7y Inspection. Although it includes information on both red meat and poultry, it
illustrates the diversity of microbial agents that may be present in or on meat and meat
products.
Salmonella and Campylobacter jejuni are generally regarded as posing the major
microbiologic risks associated with meat and poultry. However, we currently lack the
epidemiologic data necessary to calculate the proportion of human infections due to
these organisms that are attributable s~ecificaliv to red meat (i.e.. attributable risk
data). In unpublished data from the USDA National Surveillance Survey made
available to the committee (see Appendix B), Salmonella were isolated from 1.~% of
5,319 frozen red meat samples tested; the significance of these results is unclear, since
complete details on study methodology were not available. Recent concern has also
focused on contamination of meat by enterohemorrhagic strain of Eschenchia colt, a
newly described human pathogen that can cause hemorrhagic colitis and, in severe
cases, the hemolytic-uremic syndrome.
Risks associated with toxicologic hazards appear to be smaller. However, they
have been less well defined and often do not have the immediately obvious health
consequences of bacterial or viral infections.
. , ~,
, a,
. .
These observations led successive FNB committees to recommend that the Food
Safety and Inspection Service (FSIS) intensify its efforts to control and eliminate
contamination by microorganisms that cause disease in humans and optimize its
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Table 5-} Classification of Worldwide Meatborne and
Pathogens According to Modes of Transmissiona
Poult~yborne Microbial
Pathogenic microorganisms transmissible to humans by ingestion of raw or undercooked meat and
poultry:
Bacillus anthracis
Balantidium cold
Campylobacter cold
Campylobacter fetus subsp. fetus
Campylobacter jejuni
Escherichia cold
Francisella tularensis
Salmonella spp.
Sarcocystis spp.
Taenia saginata
Taenia solium
Toxoplasma gondii
Trichinella spiralis
Yersinia enterocolitica
Yersinia pseudotuberculosis
Pathogenic microorganisms transmissible to humans by ingestion of cooked or otherwise heat-processed
meat or poultry that became contaminated after the heat processing or that was improperly stored after
initial heat processing:
Any of the above
Bacillus cereus
Clostritlium botulinum
Clostridium perfringens
Shigella spp.
Staphylococcus aureus
Streptococcus pyogenes
Pathogenic microorganisms transmissible by contact with animal tissue or by inhalation of aerosols or
dust from animals:
Bacillus anthracis
Brucella spp.
Chlamydia paittaci
Cowpox virus
Coxiella burnetii
E,ysipelothruc rhusiopathiae
Francisella tularensis
Leptospira spp.
Listeria monocytogenes
Newcastle disease virus
Pseudomonas mallet
Streptococcus pyogenes
Toxoplasma gondii
Other bacteria sometimes on meat and poultry that have been reported to be pathogens but for which
proof is lacking that meat and poultry are vehicles:
Aeromonas spp.
Bacillus licheniformis
Citrobacter spp.
Klebsiella spp.
Plesimonas shigelloides
Proteus spp.
Providencia spp.
Streptococcus faecalis
Streptococcus faecium
a Source: NRC, 19SSa.
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National Residue Program (NRP) for dealing with toxicologic risks (NRC 1985a,
1987a). When the SIS-C program is considered in this context, several questions arise.
Some of these issues are dealt with elsewhere in this report, but the committee believes
that they are important enough to warrant repeating in this chapter.
Have previous FNB recommendations concerning microbiologic and toxicologic
hazards been integrated into SIS-C?
According to FSTS, the microbiologic or toxicologic issues discussed in previous
FNB reports are not directly addressed in SIS-C.
Might SIS-C have an indirect effect on microbiologic or toxicologic hazards in
red meat?
Modifications in inspection procedures could result in reduced microbial
contamination of carcasses only if they lead to improved handling of carcasses or plant
sanitation. Thus, evaluation of inspection systems should consider possible effects on
total microbial counts, and on detection and counts of such pathogens as Salmonella,
Campylobacter, and enterohemorrhagic Eschenchia cold
It is unlikely that improved inspection procedures could lead to reduced levels of
toxicologic or chemical hazards. However, any changes in carcass rinses or equipment
sanitizing chemicals should be evaluated for possible effects of these contaminants on
human health.
Are there data documenting the effects of STS-C on microbiologic or
toxicologic hazards?
FSIS data on microbiologic and toxicologic hazards are available for some
individual plants. Unfortunately, existent data sets are construed inconsistently and
appear to be too small to permit meaningful statistical comparisons between SIS-C and
traditional systems. Such confounding variables as differences in source and type of
cattle also complicate the analysis. The committee received USDA data on only 35
SIS-C samples from five SIS-C plants (see Appendix B). No conclusions about
inspection systems could be drawn due to the small sample size, low frequency of
contamination, and the freezing of specimens for shipment. Comparable problems
arise in trying to draw conclusions from available toxicologic data.
Some processing plants (such as the Monfort plant in Greeley, Colorado) have
developed data bases on microbial contamination of products. These data are of
interest, and their generation should be encouraged. However, industry-derived data
can not be substituted for substantive, statistically valid FSIS data that are subject to
the scrutiny of scientific peer review processes.
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Representative terms from entire chapter:
red meat
If there is a need for such data, how could they be obtained?
There is need for data on microbiologic and toxicologic hazards in meat to
address the committee's concerns and those of the public. These data would permit
comparisons among various inspection systems and continuing assessment of inspection
strategies in any one plant.
Relatively simple studies could be designed to provide these basic data and to
test appropriate hypotheses. For example:
o Hypothesis I: The bacterial contamination (i.e., total plate counts, Salmonella
counts, etc.) of carcasses in SIS plants is no different--neither greater nor less-
-than that of traditionally inspected carcasses of similar source and type
slaughtered under similar conditions.
O Hypothesis 2: Bacterial contamination does (or does not) correlate with
carcass error rates, as determined by organoleptic techniques.
O Hypothesis 3: Bacterial contamination rates are (or are not) more dependent
on line speed than on inspection strategy.
To evaluate these hypotheses statistically, it would be desirable to determine the
sample sizes required to provide acceptable alpha(
into ongoing studies of the relationship of antimicrobial use to drug resistance in
pathogens isolated from foodborne disease outbreaks in humans (IOM, 1989~.
Realistic and appropriate standards to protect public health are complex but
very important. Under favorable conditions, pathogenic bacteria multiply rapidly to
levels adequate to cause human disease both in the plant and after the carcass enters
the market. Therefore, microbiologic standards must be considered carefully. The zero
risk concept may be appropriate to consider as an idealistic goal for pathogenic
bacteria (which crow and multiolv1. Thus. the detection of low levels of
~ _ . .', ,
· . . .
microorganisms can be important, because such organisms can multiply rapidly to levels
adequate to cause illness in humans.
On the other hand. the negligible risk standard can be an appropriate goal for
levels of toxins or chemicals (NRC, 1987b), because their concentrations do not
increase. In fact, levels of chemicals in food are usually substantially reduced by food
processing and food preparation. Further research is needed on establishing negligible
risk levels for chemicals in food to ensure that sensitive population subgroups, such as
infants, children, or immunocompromised people, are not susceptible to risks from
chemical levels that would be safe for most people. Specific issues related to the
effects of pesticides on infants and children are currently under study by a National
Research Council committee in the Board on Agriculture. This report will be released
in 1991 (NRC, in press).
FSIS is not authorized to conduct basic research. Therefore, the necessary
studies must be done by researchers outside FSIS. However, USDA must realize that
a modern, scientifically based inspection service must conduct or fund research to
evaluate practical problems. Modernization of inspection requires sophisticated
computer systems, computer modeling, rapid diagnostics, and the ability to integrate
this technology into on-line inspection strategies.
In summary, ongoing assessment of microbiologic and toxicologic hazards
through well-designed and scientifically valid studies is essential to meat inspection.
Results of these assessments must be considered in any comparison of inspection
strategies.
Recommendations
o Microbiologic, toxicologic, and chemical data must be considered by FSIS in
designing and evaluating any inspection systems designed to protect public
health.
o
If FSIS is to develop sound, believable, scientifically based inspection strategies,
a research group must be established with the appropriate statistical,
epidemiologic, microbiologic, and toxicologic expertise to frame and test
hypotheses relating food inspection to microbiologic and chemical hazards. This
46
group should be based in USDA. It must have the flexibility to coordinate with
other government agencies (e.g., the Food and Drug Administration and the
Centers for Disease Control) involved in maintaining the safety of the food
supply. It must also have adequate funds to draw on expertise from outside the
government (i.e., universities and private industry).
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