Extension Specialist Discusses Fishing For A Safe Seafood
Wednesday, March 5, 1997
FORT COLLINS--Every day in the United States,
hundreds--perhaps thousands--of people get sick as a result of
eating seafood. For most, it's an inconvenience, maybe an
unpleasant day or two of diarrhea and stomach cramps. Others are
disabled for weeks or even years. A small number, mostly those
who eat raw shellfish, die.
"The biggest seafood hazard by far is raw or undercooked
shellfish," said Heather Hart, Colorado State University
Cooperative Extension food-safety specialist. "According to the
Food and Drug Administration, about 20 million Americans consume
raw shellfish, which accounts for over 90 percent of seafood
poisoning cases."
When you eat raw shellfish, Hart noted, you eat the whole
organism, including its gastrointestinal tract. Furthermore,
shellfish feed by filtering two to three gallons of water every
hour, which means they take in whatever is floating by, including
plankton along with viruses, bacteria, mercury and other nasty
surprises. Awaiting you in your next oyster, mussel, or clam
could be any one of the following.
Norwalk virus: The most common cause of shellfish poisoning
comes from human sewage. The virus causes nausea, vomiting, or
diarrhea. Most of the 100,000 or so people attacked each year
typically recover in a day or two.
Hart noted you can't see or smell Norwalk. "Nor does stewing
or steaming necessarily solve the problem," she said. "We know
high degrees of heat clearly can kill it and low degrees of heat
don't. But we do not know how high the cooking temperature must
be to kill Norwalk virus."
Vibrio: The worst strain, Vibrio vulnificus, thrives in the
Gulf of Mexico and kills about 10 to 15 people each year. Every
case traced by the Center for Disease Control since 1990 came
from raw shellfish harvested in the Gulf.
Only a small percentage of the population is susceptible to
Vibrio vulnificus infections, but about half of those who get it
die. The most vulnerable are those suffering from liver disease,
liver damage caused by excess alcohol or iron-overload disease
(hemochromatosis), and people with diabetes, AIDS, or cancer.
"Heat does destroy Vibrio," Hart said. "As long as you avoid
raw or undercooked Gulf Coast shellfish, especially from May
through November when waters are warm, you'll probably be safe."
Ciguatera: This is the most common fin-fish poisoning in the
United States. Some 8,000 Americans are stricken each year by
the ciguatera toxin, which is produced by plankton that grow on
tropical reefs. Small fish that eat the plankton also eat the
toxin, and large predatory fish that eat the small fish end up
carrying even more ciguatera. In the United States, ciguatera
poisoning cases are concentrated in Florida, Hawaii, Puerto Rico,
the Virgin Islands and Guam.
"Early symptoms can mimic any kind of food-borne illness,
typically nausea, abdominal cramps and diarrhea," Hart said.
"Later, a 'pins-and-needles' sensation occurs around and inside
the mouth and in the hands and feet. Victims often experience
'temperature reversals,' where hot things feel cold and, more
likely, cold things feel hot."
Effects of ciguatera usually last about two weeks, but Hart
noted "as many as 20 percent of all victims will still have some
symptoms at six months and 5 percent at two years." Because of
ciguatera's neurological symptoms, doctors have been known to
misdiagnose it as multiple sclerosis.
To avoid ciguatera, "don't eat barracuda, no matter where
you are," warned Hart. "If you're visiting the Bahamas or the
Caribbean, pass up grouper, red snapper or any fish dish like
bouillabaisse when you don't know the ingredients. In the States,
if you want grouper or red snapper, stick to smaller, younger
specimens, which haven't accumulated as much toxin."
Scombroid poisoning: Less common and less serious than
ciguatera, Scombroid poisoning occurs when certain fish aren't
kept cool enough. Bacteria on the fish create large amounts of
histamine, which can cause tingling and burning sensations around
the mouth as well as diarrhea, cramping and an itching rash.
Symptoms seldom last more than a few hours.
In the United States, mahi mahi or fresh tuna are the most
likely sources of Scombroid poisoning.
Chemical contaminants: Harmful metals, industrial chemicals
and pesticides such as mercury, PCBs, dioxin and chlordane often
wash into rivers, lakes and oceans. Forty-seven states currently
post fish consumption advisories that warn about eating certain
species. The advisories cover 1,740 rivers and lakes, including
all of the Great Lakes and large sections of coastal areas. The
most common reason for consumption advisories is mercury. In
large amounts, the metal can cause brain and nerve damage,
especially to fetuses and young children.
Large fish like fresh tuna and swordfish have the highest
levels of overall chemical contamination. A new study from the
Seychelles Islands off East Africa's coast concluded chemical
contamination in those fish doesn't appear to cause problems.
Researchers at the University of Rochester said children of
mothers who consumed a lot of these chemically contaminated fish
during pregnancies didn't show any signs of harmful effects, at
least up to age two and a half. The team is continuing to monitor
the children.
While there may be little evidence that people get enough
mercury or other contaminants from fish to suffer short-term
harm, Hart noted there might be subtle, adverse neurological
problems over the long term that scientists aren't noticing. A
recent study supports this point. Researchers tested children of
women who ate at least 4 pounds a year of PCB-contaminated fish
from Lake Michigan for six years before giving birth. The
children, now 11 years old, are more likely to have lower IQS and
to lag behind peers in reading comprehension.
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