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Vibrio parahaemolyticus

oysters Vibrio parahaemolyticus is a naturally occurring bacterium in sea water. Its numbers increase when water temperature rises during the summer months. The bacteria may grow in molluscan shellfish such as clams, oysters and mussels when seawater temperatures are warmer and then, when those shellfish are eaten raw or undercooked,  a foodborne illness may occur. The largest outbreak of V. parahaemolyticus in BC history occurred in 2015, when 62 persons became ill. 

Information for Health Professionals

Vibrio parahaemolyticus is commonly found in seawater. Most infections occur during summer and fall months when Vibrio counts in seawater are highest. Most of the time, gastroenteritis follows ingestion of undercooked seafood, especially shellfish.


Diarrhea is the most common syndrome and is characterized by:

  • acute onset of watery stools and
  • crampy abdominal pain.

The following may occur:

  • nausea
  • vomiting
  • fever
  • headache
  • bloody stools

The time from infection to symptoms is from 12 to 24 hours, but can range from four to 96 hours. The illness usually is self-limiting and lasts around three days but may last for one week.

V. parahaemolyticus grows naturally in coastal waters, and can grow to large numbers when the ocean is warm. Bivalve molluscan shellfish (i.e. oysters, clams, cockles, scallops and mussels) are filter feeders, straining out plankton and bacteria to eat. If the numbers of V. parahaemolyticus are high in the shellfish when harvested, or when shellfish are not kept cold after harvesting, and the shellfish are then undercooked or eaten raw, illness can occur. The illness is not spread from person to person.  

Infections affecting other parts of the body and death can occur, but rarely.

Your doctor may ask for a stool sample, which would be cultured for V. parahaemolyticus.

Most episodes of diarrhea are mild and self-limited and do not require any treatment other than oral rehydration. In some instances, the doctor may prescribe an antibiotic.

Purchase bivalve shellfish and seafood from reputable sources and keep them cold (below 4ºC). Only shellfish from approved sources should be eaten. (Commercial operators and recreational harvesters, see Shellfish Safety.)

  • Refrigerate these foods immediately after purchase.
  • Keep raw bivalve shellfish separate from cooked foods and follow good hygiene practices.
  • It is best to thoroughly cook oysters, clams, cockles, scallops and mussels to minimize the chances of foodborne illness.

Guidelines for cooking:

  • Boil: add shellfish in the shell to water that is already boiling. Boil for three to five minutes after the shells are open.  
  • Steam: for four to nine minutes. Throw out any shellfish with unopened shells.
  • Fry:  for at least three minutes at 190ºC (375ºF).
  • Bake:  for at least 10 minutes at 230ºC (450ºF).

SOURCE: Vibrio parahaemolyticus ( )
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