Here's the part that freaked me out: blood clams filter 40 liters of sea water per day, a larger amount than most shellfish. This means if they are harvested from areas that do not practice standard sanitary regulations, the clams absorb harmful bacteria and viruses such as hepatitis, typhoid or dysentery. Research has found that the hepatitis virus can survive for as long as three months in the clams.
They are currently banned in China as blood clams harvested in China were responsible for a hepatitis outbreak. It is illegal to import Chinese blood clams in the United States, but smugglers still manage to get them in, and there have been crackdowns and arrests in New York City's Chinatown on discoveries of seafood shops selling illegal Chinese-harvested blood clams.
Blood clams from other locations are okay, just not the ones from China or Southeast Asia. Since I have no idea where the blood clams I purchased came from, I decided against eating them, just to be on the safe side. Scary!
Related: Use Caution When Eating Escolar
(Images: Kathryn Hill)