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Frequently Asked Questions
What
is Vibrio vulnificus?
Vibrio vulnificus is a bacterium in the same family as
those that cause cholera. It normally lives in warm seawater and
is part of a group of vibrios that are called "halophilic"
because they require salt.
What
type of illness does V. vulnificus cause?
V. vulnificus can cause disease in those who eat eat
contaminated seafood or have an open wound that is exposed to
seawater. Among healthy people, ingestion of V. vulnificus
can cause vomiting, diarrhea, and abdominal pain. In immunocompromised
persons, particularly those with chronic liver disease, V.
vulnificus can infect the bloodstream, causing a severe and
life-threatening illness characterized by fever and chills, decreased
blood pressure (septic shock), and blistering skin lesions. V.
vulnificus bloodstream infections are fatal about 50% of
the time.
V. vulnificus can also cause an infection of the skin
when open wounds are exposed to warm seawater; these infections
may lead to skin breakdown and ulceration. Persons who are immunocompromised
are at higher risk for invasion of the organism into the bloodstream
and potentially fatal complications.
How
common is V. vulnificus infection?
V. vulnificus is a rare cause of disease, but it is also
underreported. Between 1988 and 1995, CDC received reports of
over 300 V. vulnificus infections from the Gulf Coast
states, where the majority of cases occur. There is no national
surveillance system for V. vulnificus, but CDC collaborates
with the states of Alabama, Florida, Louisiana, Texas, and Mississippi
to monitor the number of cases of V. vulnificus infection
in the Gulf Coast region.
How
do persons get infected with V. vulnificus?
Persons who are immunocompromised, especially those with chronic
liver disease, are at risk for V. vulnificus when they
eat raw seafood, particularly oysters. A recent study showed that
people with these pre-existing medical conditions were 80 times
more likely to develop V. vulnificus bloodstream infections
than were healthy people. The bacterium is frequently isolated
from oysters and other shellfish in warm coastal waters during
the summer months. Since it is naturally found in warm marine
waters, people with open wounds can be exposed to V. vulnificus
through direct contact with seawater. There is no evidence for
person-to-person transmission of V. vulnificus.
How
can V. vulnificus infection be diagnosed?
V. vulnificus infection is diagnosed by routine stool,
wound, or blood cultures; the laboratory should be notified when
this infection is suspected by the physician, since a special
growth medium can be used to increase the diagnostic yield. Doctors
should have a high suspicion for this organism when patients present
with gastrointestinal illness, fever, or shock following the ingestion
of raw seafood, especially oysters, or with a wound infection
after exposure to seawater.
How
is V. vulnificus infection treated?
V. vulnificus infection is treated with antibiotics.
Doxycycline or a third-generation cephalosporin (e.g., ceftazidime)
is appropriate.
Are
there long-term consequences of V. vulnificus infection?
V. vulnificus infection is an acute illness, and those
who recover should not expect any long-term consequences.
What
can be done to improve the safety of oysters?
Although oysters can be harvested legally only from waters free
from fecal contamination, even legally harvested oysters can be
contaminated with V. vulnificus because the bacterium
is naturally present in marine environments. V. vulnificus
does not alter the appearance, taste, or odor of oysters. Timely,
voluntary reporting of V. vulnificus infections to CDC
and to regional offices of the Food and Drug Administration (FDA)
will help collaborative efforts to improve investigation of these
infections. Regional FDA specialists with expert knowledge about
shellfish assist state officials with tracebacks of shellfish
and, when notified rapidly about cases, are able to sample harvest
waters to discover possible sources of infection and to close
oyster beds when problems are identified. Ongoing research may
help us to predict environmental or other factors that increase
the chance that oysters carry pathogens.
How
can I learn more about V. vulnificus?
You can discuss your medical concerns with your doctor or other
health care provider. Your local city or county health department
can provide information about this and other public health problems
that are occurring in your area. Information about the potential
dangers of raw oyster consumption is available 24 hours a day
from the FDA's Seafood Hotline (telephone 1-800-332-4010); FDA
public affairs specialists are available at this number between
12 and 4 p.m. Monday through Friday. Information is also available
on the world wide web at:
http://vm.cfsan.fda.gov.
Some tips for preventing V. vulnificus infections, particularly
among immunocompromised patients, including those with underlying
liver disease:
- Do not eat raw oysters or other raw shellfish.
- Cook shellfish (oysters, clams, mussels) thoroughly:
- For shellfish in the shell, either a) boil until the shells
open and continue boiling for 5 more minutes, or b) steam until
the shells open and then continue cooking for 9 more minutes.
Do not eat those shellfish that do not open during cooking.
Boil shucked oysters at least 3 minutes, or fry them in oil
at least 10 minutes at 375°F.
- Avoid cross-contamination of cooked seafood and other foods
with raw seafood and juices from raw seafood.
- Eat shellfish promptly after cooking and refrigerate leftovers.
- Avoid exposure of open wounds or broken skin to warm salt
or brackish water, or to raw shellfish harvested from such waters.
- Wear protective clothing (e.g., gloves) when handling raw
shellfish.
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