Massive Recall Related to Listeria Outbreak Highlights Difficulty in Tracking Outbreaks

— -- A massive voluntary recall of multiple food items that was implemented after a relatively small listeria outbreak has highlighted how epidemiologists are now using DNA to connect seemingly unrelated infections and improve food safety, according to food safety experts.

Earlier this month, CRF Frozen Foods of Pasco, Washington, expanded a voluntary food recall related to a listeria outbreak to include "all of the frozen organic and traditional fruit and vegetable products manufactured or processed in CRF Frozen Foods' Pasco facility since May 1, 2014."

The recall includes 358 consumer products sold under 42 separate brands, according to a company statement announcing the voluntary recall on the U.S. Food and Drug Administration's website.

An investigation launched by the U.S. Centers of Disease Control and Prevention found that at least eight people had been hospitalized in relation to the outbreak that started in the fall of 2013 and that CRF Frozen Foods was the likely source of the outbreak. Of those sickened, two died, though the CDC said that listeria was not the direct cause of their deaths.

A full list of all products affected by the recall is at the FDA website and the plant is currently closed as inspectors search for a source of the outbreak, according to a spokesman for CRF Frozen Foods.

"In the next couple of weeks they'll start sterilizing the plant," CRF Frozen Foods spokesman Gene Grabowski told ABC News today. "Once the sterilization process is over they'll call in the FDA inspectors and they'll examine the plant and send swabs to lab."

It could take weeks for the investigation, sterilization and inspection are completed, he said.

Food experts told ABC News that the duration and expanse of the recall is striking, but the fact that the recall was initiated after a relatively small outbreak shows new tools are getting better at catching food-borne outbreaks that might strike just a few people in different states.

Tim Jones, a food safety expert and epidemiologist with the Tennessee State Department of Health, said that this kind of outbreak is often a "nightmare" for epidemiologists looking for a source since listeria can incubate for up to 72 days.

"It affects pregnant women and infants and the elderly and immuno-compromised," explained Jones, who is not involved in the investigation. "Try to ask anyone what they ate a month ago [or] try to interview someone in a nursing home or someone who is debilitated, it’s nearly impossible."

Additionally, he said it's an incredibly complex task to find a source of an outbreak when multiple foods are involved from multiple brands because patterns are very hard to find.

"To put all of this together and trace it back to a single producer -- it's a nightmare," Jones said.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University School of Medicine, said the introduction of whole genome testing of bacteria and other infectious disease has allowed experts to identify "molecular fingerprints" in their database that help them determine the origin of an outbreak.

"I’m sure at the CDC the computers are trying to put together the molecular fingerprints of other listeria they have discovered," Schaffner said. "This is very likely another example of ... how our improved and constantly enhancing detection mechanisms actually determined an outbreak."

Bill Marler, a Seattle-based food safety lawyer, said this use of genome testing has helped uncover major outbreaks in the past, including the Bluebell Ice Cream outbreak that was connected to at least 10 listeria infections.

"That is what is connecting the dots," Marler told ABC News of the genome testing. "They are reaching back in time and finding these people" who were sick years earlier and were not yet connected to the outbreak.

Better listeria testing has helped improve safety standards in the food industry, Marler said, much as better testing in the late 1990's and early 2000's helped diminish E. coli outbreaks from ground meat.

"These kinds of technological advance will help figure out more outbreaks and will cause more recalls and when more recalls happen, the cost of the recall is expensive and that is what is going to drive industry to fix the problem before they have the problem," he said.

People most at risk of listeria infection are young children, the elderly, pregnant women or people with compromised immune systems, according to the CDC. Symptoms include fever, muscle aches, headache, stiff neck, confusion or loss of balance. The disease is especially dangerous for pregnant women, since it can lead to miscarriage, stillbirth, premature delivery, or infection of a newborn.

Of the estimated 1,600 people infected with the bacteria annually in the U.S., approximately 260 deaths occur due to listeriosis, according to the CDC.