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International Meat Topics — Volume 2 Number 6 15

by Dr Bob Mitchell, consultant to thefood sector, UK.

D

ifferent people can perceive risks invastly different ways and so this cre-ates the need for an agreed scientific

approach based on authoritative sources of information to provide a transparent evi-dence based food safety system.

Table 1 describes the salient differencesbetween biological and chemical hazards.

Biological hazards

G Bacterial infections

Live organisms invade and multiply to causedisease in the host. To initiate a foodborneinfection, sufficient viable organisms (viruses,bacteria or parasites) must be ingested in

the food.Foodborne infections that are confined to

the gastro-intestinal tract mostly present asdiarrhoeal disease together with vomitingand abdominal pain. Examples include:• Salmonella.• Campylobacter.• Escherichia coli (VTEC).• Yersinia enterocolitica.• Clostridium perfringens.

Some pathogens cause disease by spread-ing outside the gastrointestinal tract (extra-intestinal infections) into the blood or other organs in the body. Bacterial examples include:• Listeria monocytogenes.• Brucella.• Mycobacterium.

G Bacterial intoxications

Intoxications are diseases caused by theconsumption of preformed toxins in thefood. They are generally formed as a resultof growth of the organisms in processedfoods during inappropriate storage of thefood, generally involving some degree of temperature abuse.• Neurotoxins of Clostridium botulinum.• Enterotoxins of Staphylococcus aureus.• Emetic toxins of Bacillus cereus.

G Par asites and waterbor ne infectionsLive organisms invade and multiply to causedisease in the host. To initiate a foodborneinfection, sufficient viable organisms must be

ingested in the food. These are fullydestroyed by cooking so are generally asso-ciated with meats eaten raw.

Control options include inspection toremove diseased animals from the foodchain, cooking and freezing.

Examples include:• Toxoplasma, Trichinella, Taenia (tape-worm).• Cryptosporidium.• Sarcocystis.

G Prion pr oteins

Transmissible Spongiform Encephalopathies(TSEs) are a family of untreatable fatal dis-eases caused by the build-up of abnormalprion proteins in the brain and nervous sys-

tem. In humans the TSE is Creutzfeldt-JakobDisease (CJD and vCJD), in cattle it is calledBovine Spongiform Encephalopathy (BSE),or Mad Cow disease.

A similar TSE in sheep, scrapie, is notthought to be harmful to humans. There isanother variant in sheep and goats, atypicalscrapie, but there is no scientific evidencethat it is of any risk to humans.

Prion proteins are particularly stable inchemical terms and so are resistant todenaturation by chemical and physicalagents, making their destruction and dis-posal difficult. Control is by the removal of infected animals and contaminated materialsfrom the food supply.

Continued on page 16

Risk analysis for

biological and chemicalhazards in meat production

Table 1. Comparison of biological and chemical hazards.

Biological hazard Chemical hazard

Hazards can enter foods at many Hazards usually enter foods in the raw foodpoints from production to consumption or ingredients, or through certain processing

The prevalence and concentration of The level of hazard present in a foodhazard changes markedly at different after the point of introduction oftenpoints along the food production chain does not significantly change

Health risks are usually acute and result Health risks may be acute but arefrom a single edible portion of food generally chronic

Individuals show a wide variability in Types of toxic effects are generally similar health response to different levels from person to person, but individualof hazard sensitivity may differ



16 International Meat Topics — Volume 2 Number 6

G VirusesViruses are intracellular pathogens that can-not multiply outside host cells. Viruses impli-cated in foodborne diseases all have their niche in the human gastro-intestinal tractand their presence in food is a consequence

of poor hygiene through water being conta-minated with sewage or products being con-taminated by the food handler.

The diseases caused by human entericviruses fall into two major categories:• Viral gastroenteritis: Norovirus.• Viral hepatitis: Hepatitis A virus.

Other viruses of potential concern include:

G Avian inf luenzaAvian influenza, also known as bird flu, is adisease of birds caused by type A influenzaviruses which are closely related to humaninfluenza viruses. Transmission to humans in

close contact with poultry or other birdsoccurs rarely and only with some strains.The potential for transformation of avian

influenza into a form that both causessevere disease in humans and spreads easilyfrom person to person is a great concernfor world health.

In the most recent worldwide outbreak of avian influenza, 539 human cases and 318deaths due to H5N1 have been reportedfrom 15 countries which have reported out-breaks of H5N1 in poultry flocks.

To date, no epidemiological data suggestthat the disease can be transmitted tohumans through properly cooked food.

However, in a few instances, cases havebeen linked to the consumption of dishesmade of raw contaminated poultry blood.

G Pandemic (H1N1) 2009 virus (Swine Flu)

The pandemic (H1N1) 2009 virus has notbeen shown to be transmissible to peoplethrough eating properly handled and pre-pared pork (pig meat) or other productsderived from pigs. The pandemic influenzavirus is killed by cooking temperatures of 70°C, corresponding to the general guid-ance for the preparation of pork and other meat.

Risk assessment example

A risk assessment is only a tool and can beas simple or as complex as the situationdemands. Sometimes it can be as simple as‘Is the food high, medium or low risk’ or itcan be a complex multi-agency multi-national exercise looking at the risks towhole populations.

An example of the latter is the WHOListeria monocytogenes in Ready to EatFoods report. It provides an indication of the resources required to perform a formal

qualitative risk assessment as well as thetype of the outputs that can be expected.Note: this is the top of the range risk assess-ment and is the area in which governmentsand international bodies will operate.

• It was drafted by six scientists with assis-tance from seven research groups and manyreviewers from over 20 countries.• It took two years to complete and publishand is 153 pages long including appendices.

G Hazar d char acter isation

Severe illness or death in three age-based

populations were considered: prenatal/perinatal; the elderly; and an intermediateage population.

Dose-response relationships were esti-mated by using contamination and growthdata to predict levels of L. monocytogenesat the time of consumption for all ready-to-eat foods. These data were combined withepidemiology data to derive a dose-response model for each population group.

G Exposur e assessment

Exposure assessments were based on esti-mates of the frequency of contamination of

foods, the numbers of cells on ready-to-eatfoods, the amount of growth before con-sumption, the amount of each food typeconsumed at a typical serving and the num-ber of servings that were consumed per year. A survey of consumer practices, com-missioned by the meat industry for hot dogsand delicatessen meats, found that:• Most (1,300) contaminated servings of food per person per year contained lessthan one organism per serving.• 19 servings contained between 1.0 and1,000 cfu/g.• 2.4 servings contained between 1,000 and1,000,000 cfu/g.

• Less than one serving per person per year contained more than one million L. monocy-togenes.

G Risk char acterisationIndividual food category data and the dose-response model were used to estimate thenumber of cases of illness per serving andper year for each food category and eachpopulation group. The ability of a food tosupport growth of L. monocytogenes tohigh numbers and the opportunity for growth is a key risk factor in foodborne lis-teriosis.

Key findings

The model indicates that it is the few serv-ings with very high levels of contaminationthat are responsible for most of the illnessesand deaths. The vast majority of cases of lis-teriosis are associated with the consumptionof foods that do not meet the current stan-dards for L. monocytogenes in foods,whether that standard is zero tolerance or 100 cfu/g.

Chemical hazardsFinding information on actual incidentsinvolving chemical hazards is more difficultthan for biological hazards because:

G The health effects are generally not acuteand are not readily visible unless one is deal-ing with deliberate poisoning, for examplearsenic in foods or exceptional incidentswith very high levels of toxic compounds,for example mercury in fish.G People are exposed over extended peri-ods of time. The effects are chronic and so

it can take a long time for them to appear,for example cancer; or they can be difficultto define, for example behavioural prob-lems.G People tend to be exposed to chemicalhazards through their total diet and not justsome specific commodities.G Chemicals are not consumed in isolationbut in combination with many others. Thehealth ramifications of this ‘cocktail effect’are difficult to determine and are still thesubject of much scientific debate. These andother factors make detection of chemicalincidents and their epidemiological investiga-

tion very difficult.

Hazard potential

All foods are composed entirely of chemi-cals. This article will consider only thosechemicals that have the potential to producea hazard to human health.

Generally, they will be present only at verylow levels and will have been added to per-form a specific function; will arise naturally inthe food; or accidently contaminate it duringproduction, processing, packaging or stor-age.

There are potentially thousands of addi-tives and contaminants in foods. It is impos-sible to cover them all in this article. Insteadthe main generic types will be brieflytouched upon with detail being reserved for those that have recently been associatedwith meat and poultry products. Basically,there are only two types of chemical hazardin food – additives and contaminants.

The distinction between them is simple – an additive is anything that is legally deliber-ately added to a food (usually to perform aspecific function) while a contaminant is any-thing that is not.

Additives

Food additives are used to modify thecolour, flavour, shelf life or other attributesof foods. Some additives have been used for centuries, generally to preserve otherwiseperishable foods.

Strictly speaking, additives are not hazardsif they are used in foods at the levelsdescribed in legislation.

They are subject to strict regulatory con-trol and require some form of governmentapproval determining the level they can be

used and in which foods they are permitted.Labelling regulations permit consumers to

make an informed choice over whether theywant to eat foods containing additives or not.

Continued from page 15



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