Today, David Acheson, the Food and Drug Administration's assistant commissioner for food safety, told ABC News that's because the FDA has found positive salmonella tests on equipment at the plant Setton Pistachio.
The test results have prompted the company to voluntarily recall most of its products made in 2008, which were shipped out to dozens of food companies. The recall includes pistachios sent in bulk to 28 states and 14 countries outside of the United States.
The FDA cannot yet say how many additional products may be recalled, but explained that it is working with distributors and trying to get its recall list updated as quickly as possible.
Like the peanut recall, it could take months to figure out every pistachio product that might be unsafe to eat. More than 2 million pounds of pistachios were already recalled last week that came from Setton, the second largest pistachio producer in the country.
Click here for the pistachio industry's Web site, which lists products that are OK to eat.
Until now, investigators had not found positive salmonella tests at the pistachio plant. Instead, one of Setton's customers found the bacteria on some of the pistachios. The FDA announced the broadened recall on its Web site Monday night.
"So far the FDA has found two positive samples from environmental testing in the processing facility," Acheson told ABC News. Acheson also said investigators had taken hundreds of samples and could still come up with more positives.
Acheson also said those positive tests came from equipment that handles pistachios before the roasting process -- a process that is supposed to kill the bacteria. Still, he said, "It gives you a sense that the microbiological controls are not, were not where they should be in 2008."
The FDA last inspected the facility now at the center of the investigation in 2003 and found no problems. The state of California inspected the company sometime in 2008 and did not find anything alarming.
That was the case, despite the fact that Kraft Foods and the Georgia Nut Co. started getting positive salmonella tests 15 months ago on products they ultimately traced to Setton.
Mixing Raw and Roasted Pistachios Likely Compromised Food Safety
Last week, Acheson told ABC News that mixing raw nuts with roasted ones -- a major "don't" when it comes to food safety -- is believed to be the problem behind the latest nut recall.
"We've learned that on some of the lines, the firm had passed both raw and roasted pistachios and so the possibility of cross-contamination -- so that is the working hypothesis," Acheson said.
Concerns about bacteria-tainted pistachios surfaced when Kraft Foods tested them as part of a routine analysis and "found a variety of different types of salmonella."
"The fact that a customer of the company found the problem is a sign that at least somebody's watching," said Caroline Smith DeWaal, a food safety director for the Center for Science in the Public Interest. "But consumers certainly wish that the government had a more robust system so they could identify these problems before they even leave the plant."
Acheson said last week that the investigation had so far found the California plant was also testing its nuts, and did, on occasion, find salmonella.
"They had found some positives, and what they did with that was essentially put them back through the roasting process to ensure that any residual salmonella was taken care of," Acheson said.
"They are not obligated to tell FDA or anyone else if they've done that," he said.
Acheson also told ABC News that he believes the company did not do subsequent additional tests to ensure the product was safe. He added that even if it did, one negative does not mean a batch is free and clear of the bacteria.
California-based Setton International Foods Inc. sold and distributed pistachios to 36 companies nationwide. The company packs the nuts in large volume -- about 1,000 to 2,000 pounds of pistachios in each container -- and ships them to the suppliers and wholesalers that then repack or resell them to many other manufacturers under different brand names.
One of those companies was Kroger, which announced last week that it had recalled pistachios in 31 states. Kroger operates grocery stores under different names, including Kroger, Ralphs and Dillons.
The FDA announced the recall in advance of any confirmed illnesses. Last week, health officials were warning consumers to stay away from all pistachios at the early stage in the investigation.
"We just hope the FDA comes out very quickly with a more refined statement about which pistachios to avoid, because the vast majority of the pistachios are not tainted," Richard Matoian, executive director of the Western Pistachio Association, told ABC station KFSN in Fresno, Calif.
The peanut company at the heart of the recall has since filed for bankruptcy.
Peanut recalls continue to pour in eight months after illnesses first surfaced.
Symptoms of salmonella include fever, diarrhea, nausea, vomiting and stomach pain.
ABC News' Brian Hartman contributed to this report.