necessary for the host cells to die for the host
organism—in the case of humans—to
become ill (Shapton and Shapton, 1991).
Employees may serve as carriers and trans-
mit viruses to food. An infected food handler
can excrete the organism through the feces
and respiratory tract infection. Transmission
occurs through coughing, sneezing, touching
a runny nose, and from not washing the
hands after using the toilet. The inability of
host cells to perform their normal function
causes illness. After the normal function is
reestablished, recovery from illness occurs.
The inability of viruses to reproduce them-
selves outside the host and their small size
complicates their isolation from foods sus-
pected of being the cause of illness in
humans. There is no evidence of the human
immunodeficiency virus (HIV) (acquired
immune deficiency syndrome [AIDS]) being
transmitted by foods. Sanitizers such as the
iodophors can destroy viruses (see Chapter
10), but they may not be inactivated by a pH
as low as 3.0. Viruses are inactivated by 70%
ethanol and 10 mg/L free residual chlorine
(Caul, 2000).
Foodborne viruses cause diseases through
viral gastroenteritis or viral hepatitis. A virus
that has caused a major increase in out-
breaks in restaurants during the past 10
years is hepatitis A. Intravenous drug use is
one factor that accounts for some of this
rise. Infectious hepatitis A can be transmit-
ted through food that has not been handled
in a sanitary manner. The onset is 1 to 7
weeks with an average length of 30 days.
Symptoms include nausea, cramps, vomit-
ing, diarrhea, and, sometimes, jaundice,
which can last from a week to several
months. A major source of hepatitis is raw
shellfish from polluted waters. The most
likely foods to transmit viral illnesses are
those handled frequently and those that
receive no heating after handling, such as
sandwiches, salads, and desserts. Because
this disease is highly contagious, it is manda-
tory that employees handling food practice
thorough hand washing after using the toi-
let, before handling food and eating utensils,
and after diapering, nursing, or feeding
infants. Viruses also cause diseases such as
influenza and the common cold.Microbial Growth Kinetics
With minor exceptions, multiplication of
microbial cells by binary fission occurs in a
growth pattern of various phases, according
to the typical microbial growth curve illus-
trated in Figure 3–1.Lag Phase
After contamination occurs, the period of
adjustment (or adaptation) to the environ-
ment, with a slight decrease in microbial
load due to stress (Figure 3–1), followed by
limited growth in the number of microbes, is
called the lag phaseof microbial growth. The
lag phase can be extended with less microbial
proliferation through reduced temperature or
other preservation techniques. This increases
the “generation interval” of microorganisms.
Microbial proliferation is reduced through
decreasing the number of microbes that con-
taminate food, equipment, or buildings.
When initial counts of microbes are lowered
through improved sanitation and hygienic
practices, initial contamination will be
reduced; the lag phase may be extended, and
entry into the next growth phase deferred.
Figure 3–2 illustrates how differences in tem-
perature and initial contamination load can
affect microbial proliferation.Logarithmic Growth Phase
Bacteria multiply by binary fission, char-
acterized by the duplication of components
within each cell, followed by prompt separa-
tion to form two daughter cells. During
this phase, the number of microorganisms
increases to the point that, when cells divide,