FS-9
E. coliO157:H7 - Concerns and Challenges for the Next Millennium
Richard H. Linton, Ph.D. Food Safety Extension Specialist
Arun Bhunia, Ph.D. Molecular Food Microbiologist
Situation:
During the last decade, an organism called E. coli O157:H7
has surfaced as a very prominent and dangerous food contaminant. Presence of this
organism in foods has lead to nationwide food recalls, illnesses, and deaths.
E. coli O157:H7 is particularly dangerous because it has a low infective dose
(as few as 10 cells) and can lead to severe disease complications, including death.
This type of bacteria usually originates from the intestines of cattle and can
contaminate any food that comes into contact with animal waste. While several
foods can be contaminated with E. coli O157:H7, ground beef, vegetables (sprouts,
lettuce) and unpasteurized fruit juices (apple cider) are of particular concern.
Ground beef can be contaminated during the time of slaughter and fruits/vegetables
can be contaminated on the farm if they come into contact with fecal material.
More recently, E. coli O157:H7 has been associated with contaminated drinking
water.
In an effort to protect the public, E. coli O157:H7
is now considered an adulterant in ground beef. If the organism is found in
ground beef, the ground beef must be destroyed. For unpasteurized fruit juices,
a new label is required that now informs the public of the potential health
risks.
What we know:
E. coli O157:H7 belongs to a group of bacteria
called enterohemorragic Escherichia coli. Many people are curious about
how E. coli O157:H7 was named. The "O" and the '"H" represent cellular
and flagellar antigens, respectively, that are associated with the
bacterial cell. These antigens are numbered depending on certain
characteristics and this information is used to classify or name the
bacteria.
Escherichia coli is commonly found in the
intestinal tract of warm-blooded animals. Approximately 10% of the
bacteria found in the human intestine are made up of Escherichia coli.
Most Escherichia coli bacteria are harmless and help in the wellness of
human health. Fortunately, only a few types of Escherichia coli are
harmful including E. coli O157:H7.
E. coli O157:H7 is dangerous because of the disease that
it can cause. For the healthy host, disease symptoms can range from flu-like symptoms
to bloody diarrhea. However for the immuno-compromised host, the disease can lead
to a disease called hemolytic uremic syndrome that can lead to kidney failure
and sometimes death. The immuno-compromised hosts that are most vulnerable are
infants, children, and the elderly. Another concern of the infection caused by
E. coli O157:H7 is that the infective dose may be as low as 10 cells. This is
quite different compared to other disease causing organisms where the infective
dose may be in excess of a million cells.
The organism can be associated with any food that may
potentially come in contact with animal or human fecal materials. The most likely
source of contamination is the meat slaughter facility or milking operations.
However, fruits and vegetables may also be contaminated during growing, harvest,
and transportation.
Unpasteurized apple cider has been implicated as a source of contamination
and illnesses. In this outbreak, investigators believe that apples fell to the
ground where they were contaminated with animal manure. After contamination,
the apples were pressed into cider and no heat treatment was used to destroy
bacteria and ensure safety. Furthermore, these bacteria have a unique ability
to survive in acidic food environments such as apple cider (pH 3.8-4.2). More
recently, the drinking water supply was contaminated during a summer fair in
New York. The source of contamination for this outbreak was also animal manure.
Prevention and control of E. coli O157:H7 needs to
be implemented from the farm to processing to consumption. Many
prevention techniques are being studied to prevent and/or reduce
contamination on the farm including manure treatment, water treatment, and
animal feeding operations. After the farm gate, care is being taken to
ensure that transportation vehicles and processing equipment are cleaned
and sanitized effectively. Informing the consumer is also part of
prevention. Recommendations for handling meat are located on the packages
of most raw meat products. This label helps educate consumers on thawing
and cooking safely, avoiding cross contamination, and the importance of
handwashing. Unpasteurized fruit juices must also contain a label with
the following information: "WARNING: This product has not been pasteurized
and, therefore, may contain harmful bacteria which can cause serious
illness in children, the elderly, and persons with weakened immune
systems."
These methods may reduce the risk of
contamination, however, the only assurance of safety is through heating.
Fruit juices need to be heat pasteurized and hamburgers need to be cooked
thoroughly to assure that they are safe.
What we don't know:
The sudden emergence of E. coli O157:H7 is a bit puzzling.
Prior to the 1980's, the organism was not commonly associated with foods. Today,
we hear about E. coli on a regular basis. When consumers are asked what they prefer
in the foods that they eat, quality and taste often rank very high. Many consumers
prefer a juicy hamburger that is a bit red on the inside or a glass of unpasteurized
apple juice. While these foods may taste better, they also offer a higher risk
to consumers when compared to a safely cooked hamburger and heat pasteurized juice.
Several methods, other than heat processing, are
being studied to reduce and eliminate E. coli O157:H7 in food. Some of
these methods include irradiation, ozone, UV-light, high pressure and
organic acids. Due to cost restrictions and/or limited research, the
exact effectiveness of these treatments is not known. Further research is
needed.
Another challenge for E. coli O157:H7 is
detection. Since the organism can cause illness at very low levels,
microbiologists need to be able to detect very low levels of cells. This
has proven challenging to microbiologists and several methods are
currently being investigated. Ideally, microbiologists would like to have
a test that is rapid, accurate, inexpensive, and can detect as little as
one cell. Several researchers are working on optimizing microbial
detection, but we are far from reaching our goal. In addition, technology
needs to be improved where scientists can track the bacteria from farms to
processing plants to humans to effectively control the spread of this
dangerous pathogen.
There are several recommendations for reducing the
risk of E. coli O157:H7 in food. They are:
- Cook all ground beef thoroughly. Ground beef should be cooked until
the thickest part of the patty reaches at least 160F. Temperature is best
measured with an instant-read meat thermometer. After cooking, the juices
should be clear. Avoid eating ground beef patties that are still pink in
the middle.
- Consume only pasteurized dairy and fruit juice products. Avoid raw milk and
unpasteurized fruit juices.
- Wash fruits and vegetables thoroughly - especially those that will be
eaten without cooking.
- Take measures to avoid cross-contamination during food preparation and
service. Wash counters, cutting boards and utensils with hot soapy water
after they touch raw meat.
- Be sure to wash your hands prior to preparing, serving, and eating
foods.
- Drink municipal water that has been treated with chlorine or other
effective disinfectants.
- Avoid swallowing lake or pool water while swimming.
For additional food safety information about meat,
poultry, or eggs, call the toll-free USDA Meat and Poultry Hotline at
(800) 535-4555. For food safety information about seafood, diary
products, fruits, and vegetables, call the toll-free FDA Outreach and
Information Center at (888) SAFEFOOD.
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