Use caution when eating raw oysters

Not too many years ago, most oysters were eaten shucked and cooked. Now, the oyster table has turned, and the majority of oysters in Seattle-area restaurants are served on the half-shell, or raw.

Eating raw oysters, or any raw flesh, raises safety questions. Even cooked oysters (and other shellfish) occasionally harbor toxins that can make people sick.

So what's the safest way to enjoy these shellfish?

Cook them, the U.S. Food and Drug Administration flatly advises. That goes double for people with compromised immune systems, such as the chronically ill, the very old or the very young, the FDA says.

But the fact is, many people do eat raw oysters, and the number is rising.

Jennifer Tibaldi, director of food safety and the shellfish program for the State Department of Health, says raw oysters are safe to eat under controlled conditions.

"I would have no problem with eating raw oysters in any restaurant in Washington, as long as they're legally grown and harvested," said Tibaldi. "We have a very stringent program in place in regard to biotoxins."

She's confident the state's water-quality testing program and harvesting rules ensure the safety of Washington's commercially produced shellfish. She said every batch of shellfish must be tagged so the source can be traced if someone becomes ill after eating them.

"We do have people get sick occasionally," most often from the naturally occurring organism Vibrio parahaemolyticus, which sometimes infects shellfish (more on this below). But Tibaldi is unaware of any shellfish-linked deaths in Washington for many years.

Harvesting, buying and storing

Here's advice from Tibaldi and the FDA on harvesting, buying and storing live oysters for home use:

• Check the state's Marine Biotoxin Hotline or Web site (see box) before harvesting shellfish to make sure the beach where you plan to go is not closed because of biotoxins such as paralytic shellfish poison, or "red tide" (see description below). Don't rely on no-harvesting signs because they're not posted on every beach.

• Buy shellfish only from reputable dealers.

• Put oysters in an ice-filled chest immediately after harvesting or buying fresh. They should not freeze. If you're concerned they will, put a layer of newspapers between the oysters and the ice.

• Make sure unshucked, or shell, oysters, are alive before you use them; their shells should be tightly closed, not open. If they're slightly open, they should clamp shut when tapped. Discard those that don't close.

• Store oysters in the coolest part of the refrigerator and use within two days.

-• When buying shucked, jarred oysters, make sure the "sell by" date is current. The liquid should be clear or slightly opalescent, and there should be no off odor. Shucked oysters are raw and the jars unsealed. Refrigerate immediately and use within two days.

Cooking

Some harmful organisms that can infect oysters are killed by cooking, while others are not. The FDA recommends these cooking times:

• Boil live, in-shell oysters 3 to 5 minutes. Use a small pot and do not crowd in too many to avoid undercooking those in the middle.

• Steam live, in-shell oysters 4 to 9 minutes. Have the water steaming before adding oysters to steamer.

• Boil or simmer shucked oysters at least 3 minutes, or until the edges curl.

• Fry shucked oysters in oil for at least 3 minutes at 375 degrees.

• Bake shucked oysters for 10 minutes at 450 degrees.

The bad guys

Here are some organisms that can cause illness in people who eat affected oysters or other shellfish:

• Fecal coliform pollution from humans. Chief source: faulty septic-tank systems. Illness symptoms in humans: gastrointestinal distress. Killed by proper cooking.

• Vibrio parahaemolyticus, a naturally occurring organism that appears occasionally, most often in summer. Illness symptoms in humans: gastrointestinal distress. Killed by proper cooking.

• Paralytic shellfish poison ("red tide"), a naturally occurring biotoxin caused by a phytoplankton, Alexandrium catenella. Occurs most often from late spring to early October. Illness symptoms in humans: tingling in the lips and tongue, sometimes followed by nausea, general paralysis and difficulty breathing. Potentially fatal. Not destroyed by cooking.

The "red tide" nickname is misleading, experts say, because this biotoxin is only rarely associated with a red tinge to the water.

Domoic acid, also known as amnesiac shellfish poison, is another biotoxin well-known in this state. It affects razor clams but not oysters. Most common in cool-weather months, it causes gastrointestinal distress in humans or, in cases of repeated exposure, permanent short-term memory loss. Not destroyed by cooking.