WASHINGTON (Reuters) - U.S. health officials are now looking at whether humans may have consumed food containing a chemical linked to a recall of pet foods and livestock feed, the U.S. Food and Drug Administration said on Tuesday. FDA officials said they would inspect imports of six grain products used in foods ranging from bread to baby formula for traces of melamine, a chemical thought to have killed and sickened cats and dogs. The California Agriculture Department said separately it was trying to contact 50 people who bought pork that may have come from pigs fed food containing melamine. The...