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WASHINGTON (AP) _ The government has begun tougher testing for residues of an antibiotic in shrimp and crawfish following reports that some seafood with traces of the drug was shipped from China.

Chloramphenicol is a powerful antibiotic used for human infections. The United States bans its use in animals consumed by humans.

The Food and Drug Administration has long tested for chloramphenicol residues in imported seafood. But a few months ago, it received reports that Europe and Canada detected chloramphenicol in some shrimp and crawfish imported from China. The levels were lower than those FDA tests could detect.

The agency announced Friday it would tighten its testing to detect the lower levels, to stop shipments containing any drug residue at the border.

FDA officials told Chinese officials of the decision last week. China said it recently banned chloramphenicol use in animals, too, and had begun its own food testing.

It is unknown whether trace amounts of the drug in food would actually harm anyone, the FDA's Arnold Borsetti said.