FDA issues warning about paralytic shellfish poisoning. Here's what to know.

Before you dig into that platter of freshly shucked oysters or baked clams at your favorite seafood restaurant, better make sure you know from where the shellfish originated. 

The U.S. Food and Drug Administration is warning consumers to avoid eating shellfish from Oregon and Washington state because they may be contaminated with toxins that cause what's known as paralytic shellfish poisoning. At least 31 people have been sickened in Oregon so far, according to state health officials. Here's what to know about the FDA advisory.