Health officials are investigating whether humans may have consumed pork from animals that ate feed containing a chemical linked to a recall of pet foods, the Food and Drug Administration said Tuesday.
In California, traces of the chemical melamine were detected in hog urine at a farm in Stanislaus County in the Modesto area. The California Department of Food and Agriculture said it traced the hogs to several Northern California meat vendors, and most of the animals were quarantined.
Only the American Hog Farm in Ceres and a vendor in Half Moon Bay had sold the pork to customers. Both operate custom slaughterhouses that sell only to individuals for personal use -- not to supermarkets.
The department said it had been trying to contact 50 customers and said that the state health services department recommended not eating the pork. But if people did, California State Public Health Officer Dr. Mark Horton considered the health risk to be minimal, the state said.
Besides California, food safety officials have quarantined hogs at farms in New York, North Carolina, South Carolina, Utah and possibly Ohio.
"Some of the hog operations were fairly sizable," said Stephen Sundlof, director of the FDA's Center for Veterinary Medicine. But U.S. Department of Agriculture spokesman Steve Cohen said the feed was sold to smaller and independent hog farms.
A poultry farm in Missouri also may have received tainted feed, officials added.
Melamine was first found in March in wheat gluten used for some pet foods. More recently, rice protein tainted with melamine was also shipped to at least five pet food manufacturers by a supplier that imported it from China, the FDA has said.
On a conference call with reporters Tuesday, FDA officials said they would inspect imports of six grain products used in foods including bread and baby formula for traces of melamine, a chemical thought to have killed and sickened cats and dogs.
Melamine, a chemical used in plastics and fertilizer, has already been found in wheat gluten and rice protein imported from China for use in some pet foods, triggering a recall of more than 100 brands.
The FDA said it was expanding its tests as a proactive measure to ensure the safety of the human food supply. The ingredients -- wheat gluten, corn gluten, corn meal, soy protein, rice bran and rice protein -- are used in a variety of human food products, including breads, pastas, cereals as well as energy bars, meal replacement drinks and rice-based foods made for people on specialized diets.
"We're going to target firms that we know are receiving imported products," said David Acheson, chief medical officer of the FDA's Center for Food Safety and Applied Nutrition in a conference call with reporters. "The goal is obviously to sample as much as we can."
There is little research on melamine's effect on humans, according to the World Health Organization, but the chemical has been studied in animals for its risk of kidney problems and cancer. The WHO does not classify the chemical as a carcinogen for people.