Principles of Food Sanitation

1. The infecting microorganism is ingested
   and then multiplies, as is true for Salmo-
   nella,Shigella, and some enteropatho-
   genicEscherichia coli.


2. Toxins are released as the microorgan-
   isms multiply, sporulate, or lyse. Exam-
   ples of such infections are C. perfringens
   and some strains of enteropathogenic
   E. coli.

Transfer of contamination

Before a foodborne illness can occur, food-
borne disease transmission requires that sev-
eral conditions be met. The presence of only a
few pathogens in a food will generally not
cause an illness, although regulatory agencies
still consider this a potentially hazardous situ-
ation. Bryan (1979) cited several models that
have been used to support this hypothesis and
to illustrate the relationship among factors
that cause foodborne illness. Two of the mod-
els that will be discussed briefly are the chain
of infection and the web of causation.

Chain of Infection

A chain of infection is a series of related
events or factors that must exist or material-
ize and be linked together before an infection
will occur. These links can be identified as
agent,source,mode of transmission, and host.
The essential links in the infectious process
must be contained in such a chain. The
causative factors (Figure 5–1) that are neces-
sary for the transmission of a bacterial food-
borne disease are:

1. Transmission of the causative agent
   from the environment in which the food

is produced, processed, or prepared to

the food itself.

2. A source and a reservoir of transmis-
   sion for each agent.


3. Transmission of the agent from the
   source to a food.


4. Growth support of the microorganism
   through the food or host that has been
   contaminated.

Conditions such as required nutrients,

moisture, pH, oxidation–reduction poten-

tial, lack of competitive microorganisms,

and lack of inhibitors must also exist for

contaminants to survive and grow. Contami-

nated food must remain in a suitable temper-

ature range for a sufficient time to permit

growth to a level capable of causing infection

or intoxication.

The infection chain emphasizes a multiple

causation of foodborne diseases. The pres-

ence of the disease agent is indispensable, but

all of the steps are essential in the designated

sequence before foodborne disease can result.

Web of Causation

The web of causation as modified by

Bryan (1979) is a complex flow chart that

indicates the factors that affect the transmis-

sion of foodborne disease. This presentation

of disease causation attempts to incorporate

all of the factors and their complex interre-

lationships. These webs, generally oversim-

plified schematic representations of disease

transmission processes, will not be illustrated

because a very large and comprehensive fig-

ure would be required to include all patho-

genic microorganisms affecting all foods.

Contamination of foods..........................................................................

A viable way for the identification of con-

tamination sources in food establishments

is to incorporate the “zonal” approach to

Food Contamination Sources 77

Agent Source Mode Host

Figure 5–1The chain of infection.