About half of the 18,000 consumers who called the FDA reported that a pet had died, USA Today reported Monday.

However, coming up with an accurate death count requires analysis of tissue and blood samples that the FDA doesn't have.

After announcing a recall of the products made by Menu Foods, the FDA assigned 400 staff members to collect food samples, take consumer reports and monitor the recall effort, the newspaper said.

"The sad truth is that we will probably never know with any confidence the number of animals that fell victim to the pet food poisoning," FDA spokeswoman Julie Zawisza told USA Today.