San Francisco Chronicle
09-23-06
Technology, eating habits help to spread E. coli
Mass-processed foods more easily contaminated
Erin Allday, Chronicle Staff Writer
In the spring and summer of 1982, McDonald's held a special promotion -- two
burgers for the price of one -- that led to the first reported outbreak of a foodborne bacterial infection that now sweeps the nation with some regularity.
That year, at least 47 people in Oregon and Michigan, most of whom took
advantage of the promotion, fell ill with severe abdominal cramps and bloody
diarrhea. Doctors and public health investigators were spooked -- they'd never
seen anything like it.
A year later, after months of investigation by the Centers for Disease Control and
Prevention, investigators were able to identify the infection. It was a common
bacterium, one that microbiologists had long known to live in human intestinal
tracts with mostly harmless, and sometimes even helpful, results.
The bacterium was E. coli, but this was a rare strain that had mutated. It had
attached itself to a virus, and that virus made people very sick. Today, that same
strain, called 0157:H7, sickens hundreds if not thousands of Americans every
year, and is the source of the latest epidemic linked to bagged fresh spinach that
has sickened 166 people so far, one of whom died.
"At the time of that (1982) outbreak, there was no knowledge that E. coli could
cause a disease like this, so nobody believed it," said Lee Riley, a professor of
infectious disease and epidemiology at UC Berkeley who was one of the lead
investigators for the CDC in the McDonald's case and an author of the first paper
published on E. coli in the New England Journal of Medicine.
"The outbreak occurred because the restaurants were having these promotions
and going through a lot of hamburgers," Riley said. "It's the mass consumption of
meat and the way it's processed and delivered and distributed that made it
possible for this E. coli to spread."
Escherichia coli is found in everyone's body. It can be helpful -- it kills off other
harmful bacteria, for example -- but mostly it just sits there and doesn't do much.
Certain less-benign strains of E. coli are known to be the most common cause of
urinary tract infections among women.
The first noted case of 0157:H7 actually dates back to 1975, when a woman at
Alameda Naval Air Station became mysteriously sick. Doctors at the time couldn't
diagnose what ailed her, but they noted the rare E. coli found in her body and
sent a sample to the CDC. When the 1982 outbreak occurred, investigators used
that sample as further proof that E. coli was responsible for the sickness in the
McDonald's cases.
Public health officials say it's impossible to know how long E. coli 0157:H7 has
been around. People probably were sickened by it for years, or even decades,
before doctors identified it.
But the reason outbreaks have become more common in the past 25 years,
health officials agree, is because technology has been developed to identify and
connect strains of bacteria and because the nation's eating habits have changed
-- we eat mass-processed foods that make it easier for contaminated products to
reach more people.
Over the years, technology has become increasingly complex as federal health
officials searched for ways to identify outbreaks more quickly. The technique
used today, known as PulseNet, allows microbiologists to track the "paternity" of
a unique strain of 0157:H7, and, thereby, tell if isolated cases that appear around
the country are connected, said Dr. David Acheson, chief medical officer with the
federal Center for Food Safety and Applied Nutrition at the Food and Drug
Administration.
The first E. coli outbreaks in the United States were in ground beef partly
because E. coli bacteria live in cows, and partly because ground beef was
among the first food products to be highly processed and mass-distributed via
fast-food outlets. Beef from one tainted cow could be mixed with beef from
hundreds of healthy cows, and the resulting hamburger patties would all be
contaminated.
The nation has endured a handful of outbreaks since 1982 -- including one
notable outbreak involving hundreds of people who ate at Jack in the Box in 1993
-- but the meat and fast-food industries have adopted policies over the years that
make such cases more unusual now.
But in the 1990s, the source of the outbreaks spread to fruit and vegetables. In
the past decade there have been 20 such outbreaks, including the most recent
one. The last nine outbreaks involved leafy greens that were packaged into salad
mixes.
Those salad mixes have become increasingly popular as Americans, told they
need to eat more vegetables, jumped at the convenience of prewashed lettuce
and spinach. But the problem with those mixes is the same problem the meat
industry ran into -- a very small amount of contaminated vegetable can spread
the E. coli bacteria to hundreds or thousands of packages when it's mixed in a
processing plant. That was the case with bagged spinach.
"Spinach is brought in from many, many farms," Riley said. "So you have an
opportunity for a lot of bagged spinach to become contaminated. It's just a
massive spread of E. coli, even if the original contamination was limited to one
farm."
With meat, solving the problem meant simply cooking it at a high enough
temperature to kill the bacteria. But raw vegetables may prove more challenging
because there's not a lot that can be done once the produce has been
contaminated. Washing produce isn't necessarily enough to get rid of E. coli.
For now, federal and state investigators are searching farms in the Salinas Valley
for clues as to what caused the contamination in spinach. But they may never
know the answer. And to some degree, bacteria are always going to be living in
our food supply.
"We live in a microbial world," said Sam Beattie, a food safety extension
specialist at Iowa State University. "Any time you go out into an agricultural
field, can you really expect it to be a sterile environment? I don't think so."
E-mail Erin Allday at eallday@sfchronicle.com.