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TJG/TJG/ FEB 04
MEMORANDUM
TO:
DATE:
FROM:
REF:
SUBJECT: CROSS-CONTAMINATION
CROSS-CONTAMINATION
Cross-contamination is a common term for the way in which harmful food-borne
bacteria (pathogens) are passed on to humans. Indeed, for some bacteria, such as
campylobacter, it may well be one of the most important ways.
TYPES
There are three types of contamination:
a.
Bacteria, moulds or toxins
b.
Foreign bodies including insects
c.
Chemicals including pesticides and detergents.
Raw meat and poultry are the food items most likely to carry pathogens and therefore
to act as sources of organisms for cross-contamination. Surveys of fresh chickens
have shown that up to 70% may carry salmonellae or campylobacters. Although red
meat is less likely to carry such pathogens it cannot be assumed to be free of
contaminants. The wisest course is to assume that all raw meats and raw fish are
contaminated and to treat them accordingly.
Staff handling food can be a source of cross-contamination as hands are never free of
bacteria and so the importance of regular handwashing can never be overstressed as
indeed all other aspects of personal hygiene cannot.
Cross-contamination can occur via insects (flies/cockroaches), but most commonly
occurs via knives, chopping boards or other pieces of kitchen equipment. The
presence of such foreign bodies as glass or rodent droppings should be regarded with
great concern and represents a breakdown in hygiene policies and procedures.
A third area of cross-contamination is chemicals, particularly those used for cleaning
purposes. Such detergents should be appropriate for the purpose and in no
circumstances be allowed to taint the food.
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They should be properly labelled and stored. An additional area is the increasing use
of pesticides which may be found on the surface of some foods hence the need for
proper washing prior to preparation.
VEHICLES AND ROUTES
There are four main vehicles in cross-contamination:
1.
Hands
2.
Cloths and equipment
3.
Hand contact surfaces
4.
Food contact surfaces
There are two main routes by which cross-contamination can occur:
1.
Directly from one food item to another
2.
Indirectly via a vector, eg human hands, flies
As part of the training process staff should be aware of both these vehicles and routes
in order to prevent food poisoning and to apply appropriate controls. Prevention
depends on either the source of contamination or establishing barriers between them,
the vehicles and routes.
The routes of contamination can be complex and surprising. For example, an outbreak
of Campylobacter enteritis occurred in 1984 in a catering college in the south of
England. Initial interviews with patients suggested that the vehicle of infection might
be chicken but some of the patients were vegetarians who only had eaten salads.
Further investigation showed that salad had been included in all the menus but salads
are not common vectors of this disease. Investigations were undertaken in the
kitchens of the college and the route of cross-contamination was finally discovered to
be the cloths which the trainee chefs were carrying at their waists.
They had prepared New York dressed (ungutted) poultry prior to the preparation of
the salads and had been in the habit of wiping their knives on these cloths. The knives
and chopping boards had been carefully washed between each food type but the
organisms were on the cloths and contaminated the knives when they were wiped.
Any food which is to be eaten raw (such as salad) or which has been cooked and is
subsequently to be eaten cold or with only brief warming must be assumed to be at
risk of being contaminated and should be treated accordingly.
Cross-contamination can be prevented by a few common sense rules but constant
vigilance is necessary to prevent lapses which can lead to outbreaks of food
poisoning.
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A likely site for direct cross-contamination is the refrigerator or chill room. Ideally,
cooked and uncooked foods (or foods that are to be eaten raw such as salads) should
not be stored in the same area but if they are then raw meat must be:
a.
Covered with a suitable wrapping
b.
Stored in a deep pan to prevent spillage of juices
c.
Stored below cooked foods or salads
Another example was an outbreak of salmonellosis that occurred in a factory canteen.
Although no food was available for laboratory testing, investigations showed that the
infection had reached the patients in custard pies. These of course had been cooked
and no evidence could be found that there was any problem with the cooking.
However, subsequent investigations of kitchen practice showed that the pies had been
stored in a refrigerator on shelves below some chickens which had been thawing out.
Juices from the chickens had dripped onto the pies contaminating them with
salmonellae.
Even simply storing raw and cooked foods next to each other can lead to
contamination. Care must be taken in the kitchen and also in food display cabinets to
ensure that such items are correctly and adequately separated.
CONTROL
The following guidelines should be observed in order to control this problem of crosscontamination:
1.
Institute appropriate checks on suppliers and their method of food delivery
2.
Clearly separate unfit food, chemicals and refuge away from stored food
3.
Maintain a pest control programme
4.
Separate preparation areas should be used to prepare different types of food
products the same areas or surfaces should not be used for raw meat and
cooked items or salads
5.
Thaw foods in an area separate from other foods
6.
Cool foods in an area prior to refrigeration
7.
Colour coding of plastic knife handles and polypropylene chopping boards
should be used to differentiate those used for raw and cooked items; use
plastic chopping boards as it is impossible to thoroughly clean and
decontaminate wooden chopping boards
8.
Regular handwashing by food handlers must be ensured to minimise the risk
of transfer of bacteria on the fingers; handwashing is particularly necessary
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after handling raw foods, after using the toilet, and between different tasks in
the kitchen
9.
Hand drying facilities should include paper towels in preference to hot air
driers.
a. If roller towels are used they should be of the type which presents a clean
area of towel for each user (the roller towel (a loop of towelling hanging from
a roller) can cause cross-contamination and should be avoided whenever
possible)
10.
Taps on hand basins in kitchen areas should be of the elbow or preferably of
the knee or foot operated type to prevent re-contamination of hands after
washing
11.
Wash-hand basins in kitchens should never be used for the preparation of food
items or for the washing of equipment, eg knives or chopping boards
12.
Food slicers must be separate for raw and cooked items as they can act as
important vehicles of cross-contamination, particularly as they are difficult
and time-consuming to clean
13.
Protective clothing (aprons, overalls) should be changed after handling raw
meats. If subsequent preparation of cooked items or salads is required (always
remember that some apparently cooked foods are in fact raw, for example,
salamis are fermented meats, not cooked meats and should not be sliced on the
same slicer as raw meats being prepared for cooking, but should be sliced after
foods such as corned beef which is cooked in manufacture)
14.
Institute hygiene procedures to control visitors and management to the food
preparation area.
PREVENTION
Prevention of cross-contamination centres around the principles of Hazard Analysis
Critical Control Point System (HACCP). However, with respect to this section the
key theme to be identified in terms of prevention is the training of our staff during
induction, and reinforcement during the year and formalised refresher training.
Whilst it is for management in consultation with staff to establish appropriate design,
structure, layout and maintenance of food rooms and kitchens along with the right
equipment, personal hygiene including protective clothing is the responsibility of all
operational staff. Additionally, Calderdale Catering LTD establishes cleaning
procedures and pest control.
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