Vibrio parahaemolyticus

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.

What type of illness is caused by V. parahaemolyticus?

When ingested, V. parahaemolyticus causes watery diarrhoea 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.

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.

How common is infection with V. parahaemolyticus?

In Asia, V. parahaemolyticus is a common cause of foodborne disease. In the United States, it is less commonly recognised as a cause of illness, partly because clinical laboratories rarely use the selective medium that is necessary to identify this organism. Not all states require that V. parahaemolyticus infections be reported to the state health department, but CDC collaborates with the Gulf Coast states of Alabama, Florida, Louisiana, and Texas to monitor the number of cases of Vibrio infection in this region. From those states, about 30-40 cases of V. parahaemolyticus infections are reported each year. The Foodborne Diseases Active Surveillance Network, Food Net, also tracks V. parahaemolyticus in regions outside the Gulf Coast. In 1997, the incidence of diagnosed V. parahaemolyticus infection in Food Net sites was .25/100,000.

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 diarrhoea and has eaten raw or undercooked seafood, especially oysters, or when a wound infection occurs after exposure to seawater.

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 diarrhoea. In severe or prolonged illnesses, antibiotics such as tetracycline, ampicillin or ciprofloxicin can be used. The choice of antibiotics should be based on antimicrobial susceptibilities of the organism.

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.

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.

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