Summer Raises Risk For Bacteria in Oysters

Summer is here, and warmer air and water temperatures aren’t far behind. Warm water can increase levels of natural bacteria such as Vibrio parahaemolyticus (Vibrio), which can grow in oysters and make people sick if the oysters are eaten raw. Cooking oysters to a temperature of 145°F kills the bacteria, making them safe to eat.

“Vibriosis is completely preventable,” said Jerrod Davis, director of the Department of Health’s Office of Shellfish and Water Protection. “We want people to enjoy our state’s wonderful shellfish, and following some simple safety tips can help keep people healthy this summer.”

Vibriosis symptoms may include diarrhea, stomach cramps, nausea, vomiting, headache, fever, and chills. Symptoms usually appear within 12-24 hours after eating infected shellfish and usually last from two to seven days. For people with lowered immunity or chronic liver disease, vibriosis can be life threatening. 

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Also at increased risk are people who take medication to reduce stomach acid, heart or diabetes medication, or have had recent antibiotic treatment or cancer therapies; these people should not eat raw or undercooked shellfish.

Cooking shellfish until the shells just open is not enough to kill Vibrio bacteria. Shellfish should be cooked to an internal temperature of 145°F for at least 15 seconds. As a general guideline:

· If boiling, continue to cook for 3 to 5 minutes after shells open.

· If steaming, continue to cook for 4 to 9 minutes after shells open.

In addition to monitoring for Vibrio the Department of Health monitors for biotoxins such as paralytic shellfish poisoning (PSP), amnesic shellfish poisoning (ASP), and diarrehtic shellfish poisoning (DSP) that have also been found in Washington waters. These biotoxins are not destroyed by cooking.

People who eat shellfish contaminated with biotoxins can become seriously ill or even die. A person cannot tell if the toxin is present by looking at the water or the shellfish. Biotoxins such as PSP, also known as “red tide,” can only be detected by laboratory testing.

People who are harvesting shellfish can protect themselves from illness:

· Before gathering shellfish in the state people should call our toll-free, Biotoxin Hotline (1-800-562-5632) or check our shellfish safety website to see if there are any beach closures for vibrio, biotoxins, or pollution.

· Harvest shellfish from the beach as soon as possible after the tide recedes. Don’t harvest shellfish that have been exposed to the sun for more than two hours.

· Refrigerate or put shellfish on ice immediately after harvest.

· Cook shellfish to an internal temperature of 145°F for 15 seconds.