Food-Borne Diseases

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Food-borne illnesses impact the entire world. In the United States,
based on recent information from the Centers for Disease Control
and Prevention, annual incidences of food-related diseases involve
76 million cases, of which only 14 million can be attributed to
known pathogens. Food-borne diseases result in 325,000 hospitalizations
and at least 5,000 deaths per year. Since 1942, the number
of recognized food-borne pathogens has increased over fivefold!
Are these new microorganisms? In most cases, these pathogens are
simply agents that we now can describe, based on an improved understanding
of microbial diversity. Recent estimates indicate that
Norwalk-like viruses, Campylobacter jejuni and Salmonella are the
major causes of food-borne diseases. In addition, Escherichia coli
O157:H7 and Listeria are important food-related pathogens.
Many diseases transmitted by foods, or food poisonings, are discussed
in chapters 38 and 39, and only a few of the more important
food-borne bacterial pathogens are mentioned here. There are two
primary types of food-related diseases: food-borne infections and
food intoxications.

All these food-borne diseases are associated with poor hygienic
practices. Whether by water or food transmission, the
fecal-oral route is maintained, with the food providing the vital
link between hosts. Fomites, such as sink faucets, drinking cups,
and cutting boards, also play a role in the maintenance of the
fecal-oral route of contamination.

Food-Borne Infection
A food-borne infection involves the ingestion of the pathogen,
followed by growth in the host, including tissue invasion and/or
the release of toxins.
Salmonellosis results from ingestion of a variety of Salmonella
serovars, particularly typhimurium and enteritidis . Gastroenteritis is the disease of most concern in relation to
foods such as meats, poultry, and eggs, and the onset of symptoms
occurs after an incubation time as short as 8 hours. Salmonella infection
can arise from contamination by workers in food-processing
plants and restaurants, as well in canning processes.Campylobacter jejuni is considered a leading cause of acute
bacterial gastroenteritis in humans and can affect persons of all
ages. This important pathogen is often transmitted by uncooked
or poorly cooked poultry products. For example, transmission often occurs when kitchen utensils and containers are used for
chicken preparation and then for salads. Contamination with as
few as 10 viable Campylobacter jejuni cells can lead to the onset
of diarrhea. Campylobacter jejuni also is transmitted by raw milk,
and the organism has been found on various red meats. Thorough
cooking of food prevents this disease transmission problem.
Listeriosis, caused by Listeria monocytogenes (see section
39.4), is of continuing interest, as shown by the outbreak that occurred
in Southern California in 1985. This outbreak was caused
by improper pasteurization of milk used in the commercial production
of Mexican-style cheeses. At least 86 cases of infection
occurred, including 58 cases involving mother-infant pairs. Fortyseven
people died. The outbreak was traced to pinhole leaks in the
heat exchangers of a pasteurizing unit. The leaks allowed incoming
raw milk to contaminate the pasteurized milk before production
of the cheese. Listeria is difficult to work with because an extended
incubation of samples is required for growth and detection.

Foods that are transported and consumed in an uncooked
state are an increasingly important source of food-borne infection.
This is especially of concern when there is a possibility of
contact with contaminated water at any point between production
and consumption. The problem becomes more critical with increasingly
rapid movement of people and products around the
world. International trade in uncooked foods, aided by rapid air
transport, provides many opportunities for disease transmission.
Fresh foods such as sprouts, seafood, and raspberries pose significant
hazards, which will be discussed here.
Sprouts are an increasingly popular part of the new “healthy”
life-style. They are fresh, delicate and form an exciting garnish to
complement a variety of foods. Unfortunately, if these are not
germinated in pathogen-free waters and grown under sanitary
conditions, major growth of pathogens can occur. Care must be
taken especially when the seeds are germinated, because a newly
germinating seed releases organic matter and creates a spermosphere
that stimulates microbial growth in a way similar to that
which occurs in the rhizosphere. Sprouts produced in areas of the
world where there is poor control of water quality and sanitation
should be used with caution. Contaminated alfalfa, beans, watercress,
mungbean, mustard, and soybean sprouts can be major
sources of typhoid and cholera.
974 Chapter 41 Microbiology of Food
Minor errors in canning have led to major typhoid outbreaks.
In 1964 canned corned beef produced in South
America was cooled, after sterilization, with nonchlorinated
water; the vacuum created when the cans were cooled drew
S. typhi into some of the cans, which were not completely sealed.
This contaminated product was later sliced in an Aberdeen,
Scotland, food store, and the meat slicer became a continuing con-
Box 41.2
Typhoid Fever and Canned Meat
tamination source; the result was a major epidemic that involved
400 people. The S. typhi was a South American strain, and eventually
the contamination was traced to the contaminated water used
to cool the cans.
This case emphasizes the importance of careful food processing
and handling to control the spread of disease during food production
and preparation.