From the Pacific Northwest to the Florida Keys, public health officials warn of increasing dangers from foodborne bacteria in raw and undercooked oysters and other shellfish as summer approaches.

“Naturally occurring bacteria in warm coastal seawater becomes more abundant in the summer months and can concentrate in the tissues of oysters and other shellfish,” according to a recent warning posted by the Florida Department of Health.

Contaminated oysters and other shellfish do not look, smell or taste different, according to the warning.

“Each year, we see cases of foodborne illness resulting from eating raw or undercooked seafood, particularly raw oysters,” Escambia County Director John J. Lanza of the state health department said in the warning. “I cannot stress enough the importance of enjoying oysters and other seafood that are properly handled and cooked.”

Razor clam diggers in Washington state are at increasing risk of infections from handling shellfish. Photo courtesy of NOAA
Razor clam diggers in Washington state are at increasing risk of infections from handling shellfish. Photo courtesy of NOAA

In the Pacific Northwest the threat from domoic acid in shellfish doesn’t just come with the summer season. Global weather patterns such as El Nino and climate change are causing problems even during winter months. A report in January from the National Oceanic and Atmospheric Administration (NOAA) revealed the connection.

“Hazardous levels of domoic acid, a natural toxin that accumulates in shellfish, have been linked to warmer ocean conditions in waters off Oregon and Washington for the first time by a NOAA-supported research team, led by Oregon State University scientists,” according to the NOAA report.

The domoic acid levels increase with certain algae blooms that require warmer temperatures. State and federal scientists are working on better ways to predict the blooms and toxic levels of domoic acid in oysters and other shellfish.

“Advance warning of when domoic acid levels are likely to exceed our public health thresholds in shellfish is extremely helpful,” said Matt Hunter co-author of the NOAA paper with the Oregon Department of Fish and Wildlife.

“Agencies like mine can use this model to anticipate domoic acid risks and prepare for periods of more intensive monitoring and testing, helping to better inform our decisions and ensure the safety of harvested crab and shellfish.”

Until the prediction models are perfected, the best way to avoid foodborne illnesses from oysters and other shellfish is to practice good handling and cooking practices. Tips from the Florida health department are effective no matter where shellfish are harvested and eaten.

 Photo courtesy of the University of Florida
Photo courtesy of the University of Florida

Reduce your risks

  • Do not eat raw or undercooked shellfish;
  • Wash your hands with soap and water after handing raw seafood; Wear protective clothing such as disposable gloves when handling raw seafood;
  • Wash wounds and cuts thoroughly with soap and water if they have been exposed to seawater or raw seafood;
  • Avoid cross-contamination of cooked seafood and other foods with raw seafood and juices from raw seafood; and
  • Eat shellfish promptly after cooking and refrigerate leftovers.

Cooking tips for shellfish in the shell

  • Before cooking, discard any shellfish with open shells;
  • Boil until the shells open and continue boiling 5 more minutes or steam until the shells open and continue steaming for 9 more minutes; and
  • Only eat shellfish that open during cooking. Discard shellfish that do not open fully after cooking.

Cooking tips for shucked oysters

  • Boil for at least three minutes or until the edges curl;
  • Fry in oil for at least three minutes at 375° F;
  • Broil three inches from heat for three minutes; or
  • Bake at 450° Fahrenheit for 10 minutes.


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