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Division of Foodborne, Bacterial and Mycotic Diseases (DFBMD)

Vibrio parahaemolyticus

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Frequently Asked Questions

What is Vibrio parahaemolyticus?

Vibrio parahaemolyticus is a bacterium in the same family as those that cause cholera. It lives in brackish saltwater and causes gastrointestinal illness in humans. V. parahaemolyticus naturally inhabits coastal waters in the United States and Canada and is present in higher concentrations during summer; it is a halophilic, or salt-requiring organism.

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What type of illness is caused by V. parahaemolyticus?

When ingested, V. parahaemolyticus causes watery diarrhea often with abdominal cramping, nausea, vomiting, fever and chills. Usually these symptoms occur within 24 hours of ingestion. Illness is usually self-limited and lasts 3 days. Severe disease is rare and occurs more commonly in persons with weakened immune systems. V. parahaemolyticus can also cause an infection of the skin when an open wound is exposed to warm seawater.

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How does infection with V. parahaemolyticus occur?

Most people become infected by eating raw or undercooked shellfish, particularly oysters. Less commonly, this organism can cause an infection in the skin when an open wound is exposed to warm seawater.

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How common is infection with V. parahaemolyticus?

An estimated 4500 cases of V. parahaemolyticus infection occur each year in the United States.  However, the number of cases reported to CDC is much lower because surveillance is complicated by underreporting. Laboratories rarely use the selective medium that is necessary to identify this organism, and it is likely that many cases are undetected.  To improve our ability to monitor trends, infections caused by V. parahaemolyticus and other Vibrio species became nationally notifiable in 2007.  State health departments report cases to CDC, and these reports are summarized annually.  

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How is V. parahaemolyticus infection diagnosed?

Vibrio organisms can be isolated from cultures of stool, wound, or blood. For isolation from stool, use of a selective medium that has thiosulfate, citrate, bile salts, and sucrose (TCBS agar) is recommended. If there is clinical suspicion for infection with this organism, the microbiology laboratory should be notified so that they will perform cultures using this medium. A physician should suspect V. parahaemolyticus infection if a patient has watery diarrhea and has eaten raw or undercooked seafood, especially oysters, or when a wound infection occurs after exposure to seawater.

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How is V. parahaemolyticus treated?

Treatment is not necessary in most cases of V. parahaemolyticus infection. There is no evidence that antibiotic treatment decreases the severity or the length of the illness. Patients should drink plenty of liquids to replace fluids lost through diarrhea. In severe or prolonged illnesses, antibiotics such as tetracycline or ciprofloxicin can be used. The choice of antibiotics should be based on antimicrobial susceptibilities of the organism.

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How do oysters get contaminated with V. parahaemolyticus?

Vibrio is a naturally occurring organism commonly found in waters where oysters are cultivated. When the appropriate conditions occur with regard to salt content and temperature, V. parahaemolyticus thrives.

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How is V. parahaemolyticus infection prevented?

Most infections caused by V. parahaemolyticus in the United States can be prevented by thoroughly cooking seafood, especially oysters. Wound infections can be prevented by avoiding exposure of open wounds to warm seawater. When an outbreak is traced to an oyster bed, health officials recommend closing the oyster bed until conditions are less favorable for V. parahaemolyticus.

Timely, voluntary reporting of V. parahaemolyticus  infections to state health departments 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.  When notified rapidly about cases, officials can sample harvest waters to discover possible sources of infection and may close oyster beds. Ongoing research may help us to predict environmental or other factors that increase the chance that oysters carry Vibrios.

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How can I learn more about Vibrio parahaemolyticus?

You can discuss medical concerns with your doctor or other health care provider. Your local health department can provide information about this and other public health problems. Information about problems associated with raw seafood consumption can be obtained from the FDA’s Center for Food Safety and Applied Nutrition (telephone 1-800-332-4010). At this number recorded information is available on many subjects including seafood consumption and handling. A public affairs specialist is available 12:00 p.m.-4:00 p.m. Eastern Standard Time. Seafood safety information is also available on the world wide web at and There is more information about other Vibrio infections, such as Vibrio vulnificus.

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Page last modified: March 27, 2008
Content Source: National Center for Zoonotic, Vector-Borne, and Enteric Diseases (ZVED)

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