FDA Consumer:  January/February 1994
 
             How to Outsmart Dangerous E. Coli Strain
 
                       by Judith E. Foulke
 
 
Scientists have recently identified a rare but dangerous type of
the Escherichia coli bacterium. Most E. coli are harmless
inhabitants of the intestinal tract, but this variant, called E.
coli O157:H7, produces toxins in the human gut that are capable
of deadly damage.
 
On Jan. 13, 1993, a physician in Washington state reported a
cluster of children with hemolytic uremic syndrome (HUS), the
major cause of acute kidney failure in children in this country.
There was also an increase in emergency room visits for bloody
diarrhea in people of all ages.
 
Laboratory tests from the stools of infected patients showed E.
coli O157:H7. Most infected people had eaten hamburgers from
local restaurants of Jack-in-the-Box, a nationwide fast food
chain.
 
Health officials investigated the illness reports and traced the
meat in the hamburger patties to one processing plant but were
not able to determine the source of the meat. Investigators also
discovered that the patties had been undercooked at the
restaurant. Thorough cooking would have killed the bacteria, but
live, they were free to do their damage.
 
Reports of illness continued to mount and by the end of February,
three children in Washington state and one other in California
had died of HUS complications. More than 500 people from
Washington, Idaho, California, and Nevada had laboratory-confirmed
E. coli O157:H7 infections. Of those, more than 50 people had been
infected by person-to-person contact with someone who had eaten the
contaminated hamburgers.
 
As news of the outbreak spread, reports of previous food-borne
illnesses involving E. coli O157:H7 were collected and reviewed.
One outbreak in 1991, caused by contaminated fresh-pressed,
unpreserved apple cider from a southeastern Massachusetts mill,
had resulted in the hospitalization of four children with HUS.
Another 17 children required medical treatment (see "How Did It
Get in Apple Cider?").
 
Before the Massachusetts mill incident, it was not common
knowledge that this strain of E. coli could survive the acid
environment of apple cider. Scientists from the national Centers
for Disease Control and Prevention and from the University of
Georgia continued to study the cider mill outbreak, and published
a number of reports in professional journals.
 
Then, last July and August, several months after the ground beef
outbreak in the northwestern states, people who had eaten at two
Oregon restaurants of another nationwide chain became ill with
confirmed E. coli O157:H7 infections. At press time, public
health officials, including Food and Drug Administration
scientists, were trying to identify the food source of the
contamination.
 
 
Bug Not Always Bad
 
Not all E. coli are harmful. E. coli is one of several bacterial
types that are normal to the human gut and pass through the
intestinal tract with feces. It has been known for many years
that in healthy people, this group of bacteria and other normal
microbial flora reduce the chance of pathogens--harmful bacteria
that enter the body through food and water--from colonizing in
the intestines and possibly causing illness.
 
E. coli is also helpful outside the body. In food laboratories,
scientists use E. coli as an indicator of contamination, explains
microbiologist Peter Feng, Ph.D., of FDA's Center for Food Safety
and Applied Nutrition (CFSAN). If E. coli can be isolated from
the suspect food, it implies that the food is contaminated by
fecal matter, he says.
 
Research scientists also put the bug to good use in DNA studies
(see "When E. coli Is Helpful").
 
"It's because of the knowledge that E. coli is a normal
intestinal inhabitant that studies of potentially harmful strains
were delayed," says CFSAN microbiologist Joseph Madden, Ph.D. "We
now know of at least six types of E. coli, including O157:H7,
that are particularly virulent and can cause serious illness."
 
CDC first isolated E. coli O157:H7 in 1975, and in 1982
identified it as the cause of severe bloody diarrhea traced to
contaminated ground beef patties during two illness outbreaks in
Oregon and Michigan. Since then, CDC has reported about 16 major
outbreaks in the United States, with 22 deaths. Most of the
fatalities have been young children or elderly people, the two
age groups that are most vulnerable to HUS from E. coli O157:H7.
 
Reports of outbreaks are increasing, according to CDC, mostly
because of public awareness. Physicians have been alerted through
professional publications and public announcements to report
cases of bloody diarrhea, the most common symptom, to public
health officials. Such reporting helps identify clusters of
cases.
 
It is the toxin produced by E. coli O157:H7 in the intestines of
humans that damages cells of the intestinal lining. This damage
allows blood to pass into the patient's stool. Other symptoms
include stomachache, nausea and vomiting.
 
HUS develops in 2 to 7 percent of E. coli O157:H7 illnesses. In
these cases, the toxin enters the patient's bloodstream through
the damaged intestinal wall, travels to the smaller arteries that
supply the kidneys, and damages the vessels. HUS is fatal in
about 3 to 5 percent of the cases.
 
E. coli O157:H7 survive refrigerator and freezer temperatures.
Once the bacteria get in food, they can multiply very slowly at
temperatures as low as 44 degrees Fahrenheit. The actual
infectious dose is unknown, but most scientists believe it takes
only a small number of this particular strain of E. coli to cause
serious illness.
 
E. coli O157:H7 bacteria can contaminate any food. Undercooked
hamburger and roast beef, raw milk, improperly processed cider,
contaminated water, and vegetables grown in cow manure have
caused illness outbreaks in the United States. Undercooked ground
beef has been the food source in most reported cases. Harmful
bacteria that are sometimes on the surface of raw meat get mixed
through the meat in the grinding process.
 
Thorough cooking kills E. coli O157:H7. A ground beef dish will
be safely cooked when it reaches an internal temperature of at
least 160 degrees Fahrenheit. The ground beef should not be pink
in the center, and the juices should run clear. All leftovers
should be reheated to 165 F.
 
Besides food-borne transmission, E. coli O157:H7 can be passed
from one person to another or through food-to-food
cross-contamination. Thorough hand washing with soap and water after
using the toilet or changing a baby's diaper can prevent
person-to-person transmission. Proper food handling, such as not
allowing raw meat juices to mix with cooked food, will help avoid
cross-contamination.
 
 
Solving the Problem
 
Food scientists from CFSAN, USDA's Food Safety and Inspection
Service, CDC, and state health departments have been working
together to track down possible sources of transmission of E.
coli O157:H7. Public health officials first needed a laboratory
test that would specifically identify O157:H7. Available
laboratory tests identified toxins or toxin genes from E. coli
O157:H7 that are similar to Shigella bacteria, but were not
specific for O157:H7.
 
This year, FDA's Feng developed a DNA probe that reacts only with
E. coli O157:H7 and can specifically identify the organism in
about 36 hours. Though this is an improvement, scientists hope
for even better tests.
 
"Faster tests are needed, but we need technology that is more
sensitive than what we have today to create a more rapid test,"
says Feng. "The problem is that sometimes it doesn't take large
numbers of the bacteria to make people sick--it can be dangerous
in low numbers. In order to find the few cells that might be
there, we have to put the suspected contaminated food in a growth
medium for hours or days to allow the bacteria to grow. The
O157:H7 bacteria have to multiply to at least 10,000 for current
tests to 'see' them. The need for an enrichment process will
continue to slow us down until more sensitive technology is
available."
 
(For information about DNA laboratory techniques, see "High Tech
Tools for Food Safety Sleuths" in the November 1992 FDA
Consumer.)
 
USDA recently developed a Pathogen Reduction Program to
strengthen efforts to keep harmful pathogens out of the food
supply. As part of this food safety initiative, USDA is working
with CDC to identify critical control points in meat processing
at which contamination might occur. The agencies are preparing
recommendations that will help processing plants avoid
contamination at these points.
 
USDA also recently published two new regulations aimed at food
safety: One requires labeling on all raw meat and poultry
products to give consumers safe handling instructions, and the
other specifies the heat-processing, cooling, handling, and
storage requirements to be followed by processors of partially
and fully cooked uncured meat patties, including veal and pork
sausage. (At press time, enforcement of the safe handling
labeling for consumers had been delayed.)
 
In addition, USDA has asked researchers at the University of
Georgia to study the possibility of immunizing cattle against E.
coli O157:H7. Preliminary research has identified an antigen
specific to enterohemorrhagic E. coli that may be useful in
developing a vaccine.
 
Although food scientists and public health officials are
constantly improving techniques to ensure food safety, Feng
reminds consumers that raw foods will never be bacteria-free and
even cooked foods can easily be recontaminated. But proper
cooking will kill most harmful bacteria. Consumers can help guard
against food-borne illness by applying some commonsense food
safety rules for storing, cooking and serving foods. n
 
 
How Did It Get in Apple Cider?
 
Cider is often made with apples that have dropped from orchard
trees and are not aesthetically pleasing enough to be sold for
eating raw. On the ground, the apples may become contaminated
with farm animal feces or manure fertilizer. If not washed and
brushed before pressing, harmful bacteria could contaminate the
cider. This is what scientists speculate happened in the 1991
Massachusetts cider mill outbreak, in which at least 21 people
became ill. (Other apple products, such as applesauce and apple
juice, are heated during processing or pasteurizing, thus killing
the harmful bacteria.)
 
In a May 5, 1993, article in the Journal of the American Medical
Association, Richard E. Besser, M.D., and colleagues from CDC
concluded that fresh-pressed apple cider can transmit E. coli
O157:H7 and cause illness. "Risk of transmission can be reduced
by washing and brushing apples before pressing, and preserving
cider with sodium benzoate," they said. They advise consumers to
reduce their risk by only drinking cider made from apples that
have been washed and brushed.
     USDA advises that while most fresh cider on the market today
is probably safe, you may want to take extra precautions if your
family includes at-risk persons such as the very young, the
elderly, or people with immune system problems. In that case, buy
pasteurized cider or heat the cider to 160 degrees Fahrenheit (a
slow simmer, with steam starting to rise from the pan) before
serving or refrigerating. Hard cider, the kind sold in liquor
stores, is pasteurized.
 
 
When E. coli Is Helpful
 
Some types of E. coli bacteria coexist peacefully in the human
mouth and gut, and even contribute to our well-being. For
example, bacteria in our intestines produce bacteriocins,
bactericidal proteins that kill only the few organisms closely
related to the one that produced it. (Bacteriocins from E. coli
are known as colicins.) Bacteriocins, normal intestinal bacteria
and their waste products, and the lack of available oxygen
prevent other, perhaps dangerous, types of bacteria from
competing for space. Antibiotics, taken indiscriminately, reduce
the normal bacteria in the intestines, sometimes allowing
illness-producing types to get the upper hand.
 
E. coli in the gut also produce vitamins B12 and K in amounts
large enough to be valuable should the diet become deficient.
 
Starting in the 1940s, scientists began working on the genetics
and biochemistry of E. coli. That work and subsequent research
has made E. coli a very well-understood organism. Since the
1970s, when scientists discovered that genetic material could be
spliced into the bacteria and replicated, E. coli has become the
"bug of choice" for cloning genes, says FDA geneticist Thomas
Cebula, Ph.D.
 
In 1974, scientists spliced frog DNA into E. coli, and the
bacteria replicated the gene. In 1977, the first human gene was
spliced into E. coli for cloning the hormone somatostatin. In
1978, human insulin was synthesized, and in 1982, using the
cloning technique, bioengineered insulin became commercially
available. Also in 1982, a cancer gene from human bladder cancer
cells was isolated and cloned in E. coli, beginning a new
technique for cancer research. n
 
 
Quick Information
 
Information about safe handling of ground meat and ground poultry
is available from USDA's toll-free Meat and Poultry Hotline,
(1-800) 535-4555, 10 a.m. to 4 p.m. Eastern time, Monday through
Friday. Seafood safety information is available through FDA's
Seafood Hotline, (1-800) FDA-4010 (202-205-4314 in the
Washington, D.C., area), 24 hours a day. FDA public affairs
specialists can be reached from noon to 4 p.m. Eastern time,
Monday through Friday.
 
 
Judith E. Foulke is a staff writer for FDA Consumer.
 
FDA Consumer:  January-February 1994