Food poisoning and meat microbiology - Gracey's Meat Hygiene - page 257

tuberculosis (TB) caused by milk, which have often deter-
mined the procedures historically used in meat inspec-
tion, have largely been controlled. In the case of TB, this
has been achieved by reducing the infection in animals,
by identifying and removing infected animals and by
treating risk foods, for example, milk, by pasteurisation.
These traditional zoonotic diseases were usually exam-
ples where the food, meat or milk, was itself carrying the
pathogen when the animal was slaughtered or milked.
The more current problems associated with food poison-
ing are usually the consequence of the food becoming
contaminated either at the time of production or subse-
quently. This has placed an even greater emphasis on the
need for strict hygiene and temperature control . That this is
not always achieved is emphasised by the continuing and
apparently increasing problem of food-borne infections.
Not all food-poisoning organisms cause illness in ani-
mals; many bacteria are part of the 'normal' intestinal
flora, for example, Yersinia spp. and Clostridium spp. Even
with those which can cause animal illness, this may be the
exception rather than the norm. Campylobacter infection
is a good example of this, the organisms being widespread
in animals and birds yet rarely making them ill. But other
organisms, such as Salmonella spp., do cause considerable
animal ill health, although it is not usually the 'sick' ani-
mals that enter the food chain, rather recovered or carrier
animals which are still shedding the pathogen.
Most of the organisms causing problems are spread
by the faecal route, and the main problem is to prevent
food becoming contaminated with animal faeces.

Outbreak surveillance
Investigation into outbreaks can give valuable informa-
tion on the organisms involved, the food vehicles and the
factors contributing to the cause of the outbreak. The
main limitation is that the majority of cases of food poi-
soning occur as single cases or involve a single household
only, and it is much more difficult to confirm a source of
infection - even if an investigation is carried out.
Outbreaks are investigated in most parts of the world,
although there is no common approach in the way this
is performed. Lack of standardisation makes comparison
of reports from different countries very difficult, even
though the World Health Organisation and the EU have
co-ordinated programmes.
Reports of food-borne disease outbreaks within the
EU are included within the annual “European Union
Summary Reports” on zoonoses produced by the
European Food Safety Authority (EFSA) in co-operation
with the European Centre for Disease Prevention and
Control (ECDC) (www.efsa.europe.eu/en/zoonosesscdocs/
zoonosesconsumrep.htm).

General considerations
There are many and varied sources of the organisms
causing food poisoning. Most originate directly from
animals, particularly Salmonella spp., Campylobacter
spp. and E. coli. Others not only have animal sources but
survive or even increase within the environment. This
includes, for example, the Clostridia spp., Listeria spp.
and Bacillus spp. Yet others have people as the source or
reservoir - particularly Staphylococcus and viruses.
Other human gastrointestinal infections such as dysen-
tery ( Shigella spp.) can be passed by contaminated food,
although this is not the main route of spread.
Regardless of the origin of the organisms involved,
they all have one factor in common. There has been fail-
ure to adequately control the hygiene and temperature con-
trol of the whole food chain . This chain, when it involves
animals, can be divided into a number of separate stages:

Food-borne pathogens
Most cases of food poisoning are caused by bacteria
which arise from animal, human or environmental
sources. Viral infections are unlikely to be from ani-
mals and may be due to direct human contamination or
indirectly through the environment, for example, from
shellfish contaminated by discharged human sewage.
Bacterial food poisoning may take one of two forms:
infection with living organisms or intoxication with pre-
formed toxins such as with Staphylococcus aureus . The
feature which chiefly distinguishes the two types clini-
cally is the incubation period, that is, the interval
between eating the food and the development of symp-
toms. Where pre-formed toxins are present, the condi-
tions are somewhat analogous to chemical poisoning,
and symptoms will develop very rapidly, usually within a
few hours. If living organisms are ingested, time will
elapse before their multiplication in the body has pro-
ceeded sufficiently to provoke the usual reactions of
diarrhoea and vomiting.
A summary of bacterial causes of food poisoning is
given in Table 12.1.

Animal feed, for example, the feed mill
On farm, for example, suckled calves
During processing, for example, abattoir and cutting plant
Further processing and distribution, for example, butchers
Final preparation, for example, domestic or commercial
kitchen

Each of these is important in the prevention of food-
borne disease, and satisfactory practices must be in
place. No single part of the food chain bears the total
responsibility for the prevention of food poisoning.
Food-borne disease is not static and constantly changes
and evolves. The traditional illnesses such as bovine