U.S. government inspectors have begun visiting food manufacturing plants to ensure that tainted protein concentrates used in contaminated pet food have not found their way into the human food chain. 

'This is going to go on until we feel satisfied we've got it covered.'—David Acheson, U.S. Food and Drug Administration

Officials with the U.S. Food and Drug Administration said they have no reason to suspect the tainted wheat gluten and rice protein, exported from China, has been used as an ingredient in human food. The ingredients were found to be contaminated with melamine — a chemical used to make plastics and fertilizer.

"This is going to go on until we feel satisfied we've got it covered," said David Acheson, assistant FDA commissioner for food protection Thursday. "We're not setting the bar at 50 or 100 or 1,000. We're going to keep doing this until we're confident that we've got our arms around it."

More than 100 brands of pet food have been withdrawn from the marketplace since March 16.

On Wednesday, Ontario-based Menu Foods expanded its recall of wet cat and dog food because of the chance of cross-contamination.

The FDA has confirmed 16 animal deaths and has fielded about 17,000 calls from consumers about the pet food recall.

Chicken, hog feed contaminated with melamine

On Wednesday, the FDA attempted to quell consumer concerns after it was revealed that as many as three million chickens out of nine billion slaughtered may have consumed feed tainted with melamine. Earlier in the week, the agency said that hog farms in six states had also received tainted pet food for use as feed.

Officials said they would not be issuing a recall on poultry or pork products given that the feed comprised only a small portion of the chickens' diet and the risk to humans was accordingly low.

The U.S. Food and Drug Administration has confirmed 16 animal deaths and has fielded about 17,000 calls from consumers about the pet food recall.
(CBC)

Meanwhile, an FDA report indicates that Xuzhou Anying Biologic Technology Development Co. purchased the tainted gluten from as many as 25 different suppliers. The FDA said the product was not subject to export inspection by Chinese authorities because it was falsely labelled as a non-food item.

"According to the Chinese government, Xuzhou Anying did not declare the contaminated wheat gluten it shipped to the United States as a raw material for feed or food," the report said.

With files from the Associated Press