Foods that look, smell, and taste yummy can still harbor disease-causing pathogens.

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For instance, they cite unpublished data indicating that about 38 times as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

Mead et al./Emerging Infectious Diseases

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: http://www.sciencenews.org/sn_arc98/2_7_98/bob1.htm)—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 agents.

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 estimates.

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 bushy tails.'"

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 with.

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 poisonings.

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 killing microbes.

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 year.

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