By Janet Raloff
If food that was going to leave you with gut-wrenching cramps or
more tasted sickening, few people would indulge. The problem, of
course, is that sickening food can taste quite scrumptious.
Indeed, when the hour of reckoning arrives, many of us don't
suspect what hit us mistaking our discomfort for a stress
headache, bout of flu, or jittery stomach triggered by nerves.
Doctors, too, can misread the symptoms. Indeed, the surest way to
diagnose food poisoning is to test for telltale germs in the
stool of patients who report suspicious symptoms a procedure that
physicians don't routinely employ.
While all of this makes tallying the incidence of food poisoning
quite challenging, it hasn't stopped Uncle Sam from trying. Last
month, Paul S. Mead and his colleagues at the federal Centers for
Disease Control and Prevention offered up their latest estimate
in a 19-page report. Published in the September-October issue of
Emerging Infectious Diseases, it concludes that some 76 million
U.S. residents develop foodborne illness each year.
That incidence rate would indicate that on average more than one
in four people eat sickening food each year. The data also
indicate that an estimated 325,000 require hospitalization--and
almost 5,200 die--because of foodborne illness.
Where did Mead's team come up with these numbers?
They extracted confirmed cases of food poisoning from nine data
bases, such as the Foodborne Diseases Active Surveillance Network
(FoodNet) and the National Hospital Discharge Survey. In
addition, they read studies that described investigations into
particular outbreaks and the degree to which poisoning events
appear to have been underreported. Then, they multiplied the
number of known cases by the likely underreporting figure, taking
into account the different types of disease-causing agents, and
summed the totals.
For instance, they cite unpublished data indicating that about 38
times as many cases of Salmonella poisoning occur as are
reported. Because the bacterium responsible for this illness
causes nonbloody diarrhea, Mead's team multiplied the number of
cases of Salmonella poisoning and other nonbloody diarrheal
incidents by 38. Because the underreporting rate for Escherichia
coli O157:H7 which causes a bloody stool is only about half as
large, the epidemiologists upped the known incidence of bloody
diarrheal disease 20-fold.
That gave them the gross, upper estimate of incidence for
diseases caused by these germs. However, because these germs can
be transmitted by means other than food such as water
contamination they had to scale down their tally, in some cases
by around two-thirds.
What they know...
Among all illnesses linked to food, the scientists estimated that
67 percent trace to contamination with viruses such as Rotavirus,
Norwalk-like viruses, or Hepatitis A; 30 percent are caused by
bacteria, such as Salmonella, E. coli, and Campylobacter; and
less than 3 percent are caused by parasites such as
Cryptosporidium or Trichinella.
As their data show (excerpted in table, below), the most common
causes of food poisoning viruses are least likely to lead to
fatalities. Even among the other classes of disease-causing
agents, only a few stand out as being particularly deadly.
Toxoplasmosis, for instance, caused by a parasite most commonly
associated with sheep and cat feces, was linked to 20 percent of
food-poisoning deaths, while accounting for less than 1 percent
of all foodborne illness.
And Listeria a bacterium that can multiply prolifically even in
refrigerated foods (SN: 2/7/98, p. 89) caused nearly 30 percent
of food-poisoning deaths, while hardly registering as a major
source of illness. Indeed, these new data indicate that nearly
every Listeria victim requires hospitalization, and one in five
of Listeria poisonings proves fatal.
Though most people know and fear botulism, only about 60 people
in the United States contract this disease annually. That's just
2.5 percent as many people as become sickened by Listeria, and
the fatality rate is only about one-third as high as Listeria's.
Only Vibrio vulnificus, a bacterium usually transmitted by
uncooked shellfish from polluted coastal waters, is deadlier than
Listeria. This Vibrio kills almost 40 percent of its victims.
...and don't know
Unfortunately, Mead's team points out, those statistics represent
only the tip of the iceberg. The majority of food poisonings that
are characterized by acute gastrointestinal symptoms 62 million
cases, or 81 percent of all foodborne disease cannot be
attributed to known agents.
This isn't surprising, the CDC scientists point out, since many
pathogens of greatest concern today notably Campylobacter jejuni,
E. coli O157:H7, Listeria monocytogenes, and Cyclospora
cayetanesis "were not recognized as causes of foodborne illness
just 20 years ago."
The new CDC calculations suggest that more than a quarter-million
hospitalizations for acute gastroenteritis stem from food
poisoning by unknown agents. Similarly, 3,360 deaths or 65
percent of those attributable to food poisonings trace to unknown
Mead and his colleagues concede that their estimates are based on
considerable extrapolation and inference. However, they note that
these numbers are also grounded in more data than most earlier
Surprisingly, CDC's new overall total estimate of annual food
poisonings falls within just 7 percent of the 81 million cases
per year calculated by the U.S. General Accounting Office.
Interestingly, last year a reporter with the Post-Crescent in
Appleton, Wisc., set about trying to track down the basis of many
widely circulated and largely unattributed numbers quantifying
food-poisoning in the United States. Dan Wilson noted that most
news stories treated whatever number they cited as "one of those
accepted truths that require no attribution, like 'squirrels have
In the May/June 1998 Columbia Journalism Review, he described his
trek to verify those numbers and establish their source. He ended
up frustrated as he learned that most of the cited food-poisoning
stats were based on reports whose tallies were quite not firm.
CDC is similarly frustrated by the imprecise data it has to work
Things are improving, however. For instance, FoodNet, one of the
data bases on which CDC relied, has recently started collecting
data on cases of vomiting not associated with diarrhea. That
could capture many unreported episodes of acute, short-duration
Several other countries are already doing a much better job of
catching cases of food poisoning, notes Elizabeth Scott, a
consulting Boston-area microbiologist focusing on foodborne
pathogens. In Britain and Holland, for instance, physicians must
report all cases of gastroenteritis. Particularly where these
reports turn up sporadic cases, she says, one begins to suspect
food poisoning especially in the home.
In many ways, she says, the big surprise is that there isn't more
food poisoning. Her studies and those by others have shown that
people don't tend to practice good kitchen hygiene. She notes,
"People consider it common sense to use detergent and hot water
to wash cutting boards and sponges." Not so. "The detergent just
breaks up [colonies of] the bacteria and spreads them around. It
doesn't kill them," she told Science News Online.
This means that using damp sponges that have been hanging around
the sink "and cleaned with nothing more than detergent" risks
seeding counters and kitchenware with millions of potentially
sickening bacteria and viruses. Completely drying sponges and
counters or cleansing them with chlorine bleach is effective in
Indeed, a 1998 survey by the Food and Drug Administration found
that though increasing numbers of Americans are becoming aware of
food-safety issues, they continue to practice "risky behaviors."
To quantify this, FDA has begun videotaping 150 Utah residents as
they cook at home. The goal is to identify where people might be
making mistakes compromising safety without realizing it. The
findings are slated to be synthesized and published early next
Kurtzweil, P. 1999. Keeping food safety surveys honest. FDA
Mead, P.S., et al. 1999. Food-related illness and death in the
United States. Emerging Infectious Diseases.
DeWaal, C.S., et al. 1999. Food Safety Guide. Nutrition Action
Health Letter 26(October):1.
Fox, N. 1997. Spoiled: The dangerous truth about a food chain
gone haywire. New York: Basic Books.
Hingley, A. 1999. Campylobacter: Low-profile bug is food
poisoning leader. FDA Consumer 33(September-October):14.
Raloff, J. 1998. Wash-Resistant Bacteria Taint Foods  .
Science News 153(May 30):340
_____. 1998. A polished approach to food safety  . Science
News Online (Feb. 14).
_____. 1998. Staging germ warfare in foods  . Science News
_____. 1996. How to disinfect your salad  . Science News
Online (Sept. 28).
_____. 1996. Sponges and sinks and rags, oh my!  Science
News 150(Sept. 14):172.
_____. 1996. Lessons from a case of toxic ice cream  .
Science News Online (July 27).
Scott, E., and P. Sockett. 1998. How to Prevent Food Poisoning.
New York: John Wiley and Sons.
Wilson, D. 1998. Food poisonings' phony figure. Columbia
Journalism Review (May/June):16.
1996. Food safety: Information on foodborne illnesses. Report
RCED-96-96 (May). U.S. General Accounting Office, Washington, DC
Paul S. Mead
Division of Bacterial and Mycotic Diseases
Centers for Disease Control and Prevention
Mail Stop A38
1600 Clifton Road
Atlanta, GA 30333
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