Vibrio parahaemolyticus

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Vibrio parahaemolyticus, a halophilic (salt-requiring) bacterium, exist naturally in marine and estuarine environments throughout the world, including the coastal waters of the United States and Canada. The bacteria are capable of infecting marine fish and shellfish, especially oysters harvested from coastal areas.

Transmission occurs mainly via the consumption of raw, undercooked, or contaminated shellfish, particularly oysters. A higher risk of transmission has been linked to the warmer months of the year when the bacteria, which reside in marine silt during the cooler months, live freely in the water and within fish and seafood. Person-to-person transmission is rare and is fecal-oral in nature.

The bacteria are also capable of causing wound infections, which can occur either through the exposure of a new wound caused by an immediate injury or pre-existing wound to brackish, estuarine or marine waters. An infection can also occur if the wound is exposed to raw fish or shellfish, or their drippings.

Illness onset can occur between 4 to 96 hours after exposure. The intestinal presentation of the illness is typically moderate in severity and resolves within 1-7 days.

Symptoms include:

  • Watery diarrhea
  • Nausea and vomiting
  • Abdominal cramps
  • Fever and headache

Severe symptoms occur in a quarter of those affected and include:

  • Dysentery-like illness
  • Bloody or mucoid diarrhea
  • High fever
  • Elevated white blood cell count
  • Rarely- Systemic infection and death

Severe illness is more common in individuals with weakened immune systems.

Wound infections have the following symptoms:

  • Rapid development of severe infection of affected wound
  • Localized swelling
  • Anemia from red blood cell destruction
  • Low blood pressure

General recommendations for avoiding Vibrio parahaemolyticus gastrointestinal illness:

  • Implement refrigeration of seafood from harvesting/purchase to consumption.
  • Avoid the consumption of raw seafood, especially oysters, if:
    • They have come from coastal waters during the warmer months of the year
    • You have a weakened immune system
  • When preparing oysters, mussels or other molluscan shellfish-
    • Before cooking, discard any opened shells
    • Boil, broil or fry (at 375 F) for at least 3-5 minutes
    • Bake at 450 F for 10 minutes
    • As a rule - discard any unopened shells after cooking
  • Only eat shellfish or shellfish that is thoroughly cooked until steaming hot.
  • Eat shellfish immediately after cooking and refrigerate leftovers.
  • Avoid cross contaminating raw juices from seafood with other foods, and immediately cleanup any spills with hot water and soap and clean rising water.
  • Keep raw seafood separate from other food.
  • Thoroughly wash hands, utensils and surfaces after preparing or handling raw seafood.

General recommendations for avoiding wound infections:

  • Do not handle raw seafood of any kind if you have a pre-existing wound.
  • Wear protective clothing (e.g. Gloves) when handling raw seafood.
  • Avoid marine, estuarine or brackish water if you have a pre-existing wound.
  • If you sustain a wound or injury while exposed to salty seawater or while handling seafood, thoroughly clean and disinfect the area immediately and seek medical attention if the area becomes inflamed.

Recent Texas Trends
Over the last five years, 2015-2019, the average number of Vibrio parahaemolyticus infections reported in Texas has been 31 cases per year (ranging from 22 to 43). Infections also appear to be seasonal in nature, with most (67% in 2019) occurring between May and October.
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