Food Biochemistry and Food Processing (2 edition)

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41 Microbial Safety of Food and Food Products 789

Figure 41.1.On-farm sources of microbial contamination of water and food products of plant and animal origin. (Adapted from Beuchat 1995.)

SOURCES OF FOODBORNE PATHOGENS

In order to determine and implement effective control mea-

sures for pathogens in foods, it is important to identify potential

sources of contamination. Plants and animals are the main source

of human food supply. The exterior and, in some cases, the inte-

rior of plants and animals harbor microorganisms from external

sources such as soil, water, and air. These environmental sources

contain a wide variety of microorganisms, some of which are

pathogenic to man. Contamination of the food supply can occur

at various stages of production, processing, transportation, and

storage. For example, fruits and vegetables can be contaminated

at the farm level as well as during harvesting, transportation, and

processing. Potential sources of on-farm contamination of fruits

and vegetables are summarized in Figure 41.1. Meats can be

contaminated at the time of slaughter, processing, and storage.

Microbial contamination can come from slaughtered animals,

water, equipment, utensils, the slaughterhouse environment, and

workers. Thus, intervention strategies to control microbial con-

tamination of the food supply must be implemented at various

stages of food production, processing, transportation, and stor-

age, and also at the consumer end of food preparation.

FOODBORNE DISEASE CASES

AND OUTBREAKS

Foodborne disease in a susceptible host can result from con-

sumption of food or water contaminated with pathogenic organ-

isms. A single or sporadic case of foodborne illness refers to an

instance when an illness that is unrelated to other cases occurs

as a result of consumption of contaminated food or water. An

outbreak, on the other hand, refers to an incident in which two

or more persons become ill after consuming the same food or

water from the same source. The occurrence of a foodborne ill-

ness depends on a number of risk factors such as (1) type and

number of pathogenic microorganisms in the food, (2) effect

of food product formulation or processing on the viability of

the pathogen, (3) storage conditions of the food that may pro-

mote contamination, growth, and survival of the pathogen, and

(4) the susceptibility of the individual to foodborne illness. It is

believed that the number of reported outbreaks represents only

10% of the real incidence of foodborne disease, even in coun-

tries with well-established surveillance systems (Baird-Parker

2000). Foodborne illness resulting from severe infections such

as hemolytic uremic syndrome, botulism, and listeriosis often

require hospitalization and are more likely to be reported, while

self-limiting foodborne illness such as salmonellosis, campy-

lobacteriosis, andS. aureusenterotoxin–related infections are

less likely to be reported. It is believed that viral foodborne in-

fections account for a large portion of cases of foodborne illness

(Caul 2000). However, the extent of the problem on a global scale

is difficult to assess as a result of lack of surveillance data in

most parts of the world, coupled with the fact that most viral in-

fections are self-limiting. Although viruses and bacteria-related

infections account for the majority of foodborne diseases, cer-

tain groups of parasites and fungi are also etiologic agents of

foodborne diseases.

Foodborne Bacterial Infections

Several types of foodborne bacterial pathogens are implicated

in foodborne diseases. Examples of bacterial genera most com-

monly implicated in foodborne infections, onset and duration

of the symptoms of the disease, types of foods that are likely

to be contaminated by these groups of bacteria, and potential

sources of contamination are summarized in Table 41.1. Bac-

terial pathogens includingCampylobacter, Salmonella, Listeria

monocytogenes, and verocytotoxigenicE. coliare the top causes

of bacterial foodborne infections in westernized countries, based

on the number of reported cases (Sharp and Reilly 2000). The