Emerging Infectious
Diseases
Lecture 4 & Sample Questions
The importance of food borne diseases can not be
under estimated. Diseases resulting
from the consumption of food are quite common. Usually the food is contaminated
with a pathogen or a toxin and the food acts as a vehicle for the pathogen or
toxin.
The
number of cases of disease resulting from food consumption is estimated to be
between 6 and 80 million cases per year. Such a wide range exists for several
reasons:
a) Many people do not seek
medical attention because the illness only lasts for a couple of days.
b) The illness is not severe
enough to seek medical attention.
c) Those individuals that do
visit the doctor may not be willing to provide a stool sample for diagnosis.
d) Doctors may not report
the cases to recording agencies because a specific diagnosis or etiology was
not determined.
The number of individuals that die each year from food
borne disease is estimated to be around 9,000.
Food borne diseases have a negative impact on the
economy, as the ill miss work and spend money on “supportive care”. Supportive
care items would consist of antidiarrheal medication, electrolytes, and pain
relief products.
Many of the diseases associated with food borne illnesses
are acute illnesses and resolve in several days. However, some illnesses have
been associated with chronic sequella such as Guillain-Barre Syndrome in
individuals infected with Campylobacter.
Many in the health profession wonder if there is really
an increase in the number of food borne illnesses. A number of governmental agencies have set up reporting systems
in which data concerning food borne diseases is being recorded. Some feel that
the increase in cases is due to better reporting of these cases. Others feel
that there is an increased awareness by the medical as well as the private
sector and so doctors are more likely to diagnose a case of food borne illness
as compared to in the past. Considering the number of new pathogens that are
now recognized as food borne pathogens and the
frequency of reported food borne
disease epidemic outbreaks, an increase in the number of cases of food borne
related illness is most likely on the rise. Not only are there new pathogens
involved in these outbreaks such as Salmonella enteritidis, a number of well
known pathogens such as Campylobacter have been frequently incriminated in food
borne outbreaks. Likewise there have
been several factors that have developed during the past 20 years that make the
emergence of food borne disease a reality. The erst of this paper will focus on
those newly developed risk factors.
Before discussing these new risk factors, it would be
good to review the 5 basic factors that must be present in order for a food
borne disease to occur. When reading about the newly developed factors that
predispose society to food borne diseases, keep these basic factors in mind.
1. Presence of pathogenic
organisms or toxins in the food consumed
2. Source of contamination
3. Medium for the growth and
maintenance of the pathogen or toxin
4. Proper environmental
conditions to maintain or allow for replication of the pathogen
5. Consumption of a
significant quantity of the contaminated or infectious food, ie acquire an infectious
dose.
There have been several developments during the past 20
years that may account for this observed increase in food borne disease related
illnesses.
- Human demographics and behavior
- Technologies with in the food industry
- International travel and commerce
- Microbial adaptation
- Economic development and land use
- Break down of public health education
Human Demographics and
Behavior
1. The population of
immunocompromised individuals has increased. These individuals are at increased
risk of acquiring infectious agents including those harboring in food.
- estimated 1 million individuals are infected with HIV
in the US
- the number of elderly in the US society is increasing
-
the number of individuals that are receiving immunosuppressive drugs as part of
chemotherapy is increasing
- modern medicine, often times requiring techniques that
result in immunosuppresion, has
extended the life expectancy of Americans
Because immnuocompromised
individuals lack the ability to ward off infections, even opportunistic
organisms, such as Listeria, which rarely cause disease in healthy adults are
potentially potent pathogens. Likewise, the infectious dose is reduced and the
severity of disease caused by pathogens is increased in immunocompromised
individuals.
2. Consumer Behavior
Consumers are eating more fresh vegetables and fruits. As
a result, any contamination of the surfaces of these products increases the
likelihood of disease development.
Because
of the seasonality of vegetable and fruit production, many products are
imported into the US from foreign countries in order to meet consumer demands.
The growing and harvesting practices in foreign countries may not be equivalent
to those used in this country. Poor hygiene standards could potentially
increase produce contamination leading to food borne illnesses.
For health and ethical reasons, a portion of the US
population prefers organically grown produce. Since chemical fertilizers are
not used, animal manure is often used as a substitute. Since many of the food
borne pathogens are of fecal origin, the practice of using natural fertilizers
may increase fecal pathogen exposure to individuals consuming these products.
Because of an increase in expendable income and the busy
lifestyles most Americans live, more food is being consumed outside of the
home. This has certainly increased the number of cases of food borne disease as
80% of the outbreaks originate from food consumed outside of the home.
There are a number of reasons for this:
a) non-skilled workers in the restaurants
b) exposure of food to air contamination in the case of
salad and hot bars
c) improper holding temperatures
d) pooling of raw products or foods, for example
scrambled eggs and hamburger
e) incomplete cooking of product as a result of human or
cooking equipment error
3. Technologies within the
Food Industries
In the past food was produced and consumed within a
community. As communities became larger and transportation more accessible,
food was grown or processed at one point and shipped to another. Proper
shipping and handling of food are important in the prevention of food borne
disease. Shipment of foods over long
distances at inappropriate temperatures could allow for pathogen multiplication
and increase the risk of development of a food borne disease outbreak. Likewise cross contamination of prepared
product and raw product within the same transport vehicle may occur, resulting
in consumption of a contaminated food stuff.
The development of large distribution centers has
increased the number of mass distributed food products. By shipping out large
quantities from one source, contamination at that source in turn has the
potential of producing disease in thousands of individuals. An example is the
number of recalls on ground beef allotments. These allotments have been very
large consisting of thousands of tons meat.
The utilization of equipment in the procurement of a
product has increased over the years. Many carcasses may be processed by one
piece of equipment during a shift. If one carcass contaminates the piece of
equipment, any product produced after the initial contamination will be
contaminated.
The face of agriculture has changed during the past 30
years. There are fewer farms but the farms that remain are larger. As farm size
has increased, specialization and integration has occurred, with a variety of
farms being organized under a production system. The poultry industry is the
best example in which a few companies produce chicks which are then distributed
to broiler farms. Because a few farms produce the majority of chicks, if these
chicks are contaminated at the hatching farm, many farms are then contaminated
and then those contaminated chicks eventually are sent to market. Because of
this type of centralization, a disease agent could be spread through a large
portion of the animal population potentially exposing a large number of animal
products and consequently consumers.
Because a variety of hazards may occur in the development
of any product, the food industry has developed HACCP, Hazard Analysis Critical
Control Points. This analysis allows for the processor to evaluate each step of
product development and identify hazards that may occur and develop controls to
eliminate these hazards as well as develop means to monitor these critical
steps in production.
4. International travel and
commerce
International travel has increased dramatically during
the past 20 years. People traveling abroad may be exposed to food pathogens and
acquire symptoms during their travels or after arriving home. These introduced
“foreign” pathogens potentially could spread to other residents in the US
population.
Many foreign travelers visit the US for vacation, site
seeing, and visiting relatives. Often, these visitors bring foods from their
country. These foods may contain pathogens resulting in disease in those
consuming these foods. Soft cheeses from Mexico are frequently associated with
food borne disease as these cheeses are often made with raw milk.
Foods, especially raw fruits and vegetables from abroad
may be shipped to the US which contain pathogens. The growing and harvesting
practices for this produce may be very different than what is accepted as
standard in the US. The most recent problem was an outbreak of cyclosporosis
associated with raspberries from Guatemala.
With the passage of NAFTA, many foreign markets have been
opened. The main export of many
southern hemisphere countries is produce. The amount of produce and foreign
products entering the US is likely to increase. Although there is an inspection
of these imported products, the inspection process only looks at a small sample
of the total amount of product that enters the country.
5. Microbial adaptation
Just as complex organisms have adapted to changing
environments, microbes likewise have adapted.
Foods are often preserved by the use of drying, salts, chemicals, acids
and bases. Some pathogens have adapted to living in dry environments and others
can survive in acidic environments. Products that are preserved utilizing these
previuosly mentioned processes now need to be more closley monitored for the
presence of these adapted organsims.
Some organisms have become resistant to antibiotics. A
strain of salmonella, Salmonella
typhimurium DT 104 is resistant to a series of antimicrobials. This
organism was relatively rare in the early 1990’s and by 1995 was the second
most common cause of human salmonellosis in England. Antibiotics no longer eliminate these infections in animals and
as a reuslt, these animals may harbor these resistant organisms at the time of
slaughter and pass these organisms on to consumers of food animal products.
6. Economic development and
land use
As mentioned previously, the number of farms is
decreasing but the size of the farms is increasing. As a result animals are
housed more densely which increases the spread of microorganisms between
animals. Likewise manure management becomes more of a concern. Manure is
reapplied to fields but because of the amount that is generated in a small
area, the potential for run off and ground water contamination is increased.
Areas in which foods were originally harvested may no
longer support a large enough biomass to support economic harvesting. As a
result production and harvesting areas may change. An example is oyster
harvesting. Because of the declining harvesting in the Cheasapeake Bay, the
majority of oysters are harvested in the Gulf of Mexico. There has been an
increase in the number of Vibrio
vulnificus infections as prevalence of this organism in oysters increases
as the water temperature increases. Because oyster harvests have been low in
the Cheasapeake Bay, oysters are being harvested all year round from the
gulf. In the past oysters were not harvested from the gulf during
the warmer months of the year because of the increased prevalence of
Vibrio.
7. Break down of public
health education
The public health curriculum in primary and secondary
education has changed significantly during the past 25 years with the beginning
of the AIDS epidemic and the rise in teen pregnancy and drug abuse. Curricula
are focusing on these important modern public health issues. Because there is
only so much time in the curriculum, other aspects of public health are
dropped. Likewise, funding for education has been reduced resulting in less
after school programs reducing the opportunity for addressing issues that have
been dropped. Home economics is no longer taught in many schools so proper food
handling and preparation is left to home education.
The amount of instruction a child may receive at home in
regards to food safety is probably less than what it has been in the past. When
both parents work or in a single parent household, there is limited opportunity
for food safety instruction. To make matters worse, the number of meals
consumed outside the home has increased reducing the opportunity to prepare
meals and learn proper cooking skills.
Futhermore, many of today’s meals are prepared from a package and placed in the
microwave, leaving safe food preparation to the manufacturer of the product.
The emergence of food borne diseases is a result of a set
of complex issues. By understanding
these issues, one may be able to modify or alter these issues or risk factors
interrupting the development of outbreaks.
a) consumption of an
infectious dose of organisms or toxins.
b)
consumption of raw fruits and vegetables.
c) a source of
contamination.
a) Improper food handling
procedures as a result of a lack of education among the work force.
b)
Better recording systems.
c) Increased consumption of
meals outside of the home.
a) integration allows for pathogens from one source
to contaminate a whole system of production resulting in potential exposure of
consumers through that systems product.
b) integration has increased
production output and quality control has been more difficult to monitor thus
allowing inferior product to enter the market.
c) integration has required
the increase use of antibiotics to maintain production. The use of these
antibiotics has produced antibiotic resistance resulting in “Super” bugs that
are highly contagious.
a) increased consumption of
food eaten at home.
b) less expendable income,
resulting in purchasing poor quality foods.
c)
increased consumption of food eaten outside of the home.