Listeria is a stealthy, hardy foe. It can contaminate food at any point during the production process. It can survive and thrive under inhospitable conditions. It can also be deadly to high-risk groups of people who are vulnerable to its toxic effects.

Federal public-health and food-safety agencies are working to raise awareness about Listeria monocytogenes (Lm). The Atlanta-based Centers for Disease Control and Prevention (CDC) recently hosted a teleconference with officials from the US Dept. of Agriculture and the Food and Drug Administration aimed at warning consumers about the dangers of Listeria.

Listeria is a really challenging infection to fight because it can be unnoticed in factories; it can contaminate food not only in production but in processing and preparation,” said Dr. Tom Frieden, director of the CDC. “In your refrigerator, it can continue to grow, as happened in the cantaloupe outbreak. And when someone eats it, sickness or miscarriage may not occur for weeks later, when it can be quite hard to trace back and figure out what the contaminated food was.”

Symptoms of listeriosis include fever, muscle aches, diarrhea or other gastrointestinal problems, according to the CDC. But almost every listeriosis diagnosis involves an invasive infection, which typically means the bacteria have advanced beyond the gastrointestinal tract.

A CDC Vital Signs report on Listeria found 1,651 cases of listeriosis were reported nationwide during 2009-2011, and 21 percent of those patients died. Twelve reported outbreaks sickened 224 people in 38 states.

Several populations are hardest hit by Listeria. People age 65 and older are four times more likely to get Listeria. Pregnant Hispanic women are 24 times more likely to get the infection; pregnant women are 10 times more likely to become infected. People with compromised immune systems can be susceptible to Listeria infection. Roughly one in five patients infected with Listeria die from it.

Deli food safety

The CDC reports that of the 10 Listeria outbreaks with an identified food source, six were linked to soft cheese and two to raw produce. Deli meats and ready-to-eat products have been implicated in past outbreaks. Dr. Elisabeth Hagan, Undersecretary for Food Safety at the USDA, says the agency’s zero-tolerance stance toward Lm in ready-to-eat products dates back to 1989. Outbreaks in the 1990s and 2000 led the agency to take a closer look at potential food-safety gaps that were enabling the pathogen to contaminate food and infect consumers.

“The agency found that not all establishments producing ready-to-eat foods, such as deli meats or hot dogs, were adequately controlling the threat of Lm in their establishments,” Hagen says. “Specifically in areas of the plant where cooked products were processed and packaged, some steps were not taken to prevent Lm. This is important because these are products that consumers are not going to be cooking. In a raw product, the risk of illness can be reduced with safe cooking.”

Prevention-based focus

Today, cases of listeriosis are rare, but public health and food-safety agencies have pledged to remain vigilant because the consequences of infection remain high. Also, rates of Listeria infection have stalled over the last decade. The consensus among public health and food-safety officials is that more needs to be done to make progress toward lower Lm infection rates.

USDA’s Food Safety and Inspection Service and the FDA collaborated on a scientific evaluation of the risk of listeriosis associated with consumption of meats, cheeses and other ready-to-eat foods prepared in retail delis. The risk assessment included interventions that limit the growth, survival or transmission of the bacteria that cause listeriosis.

“Following implementation of this rule, the agency observed a 75 percent drop in the percentage of ready-to-eat meat and poultry products testing positive for Lm, from about 1.2 percent in 2001 to 0.3 percent in 2011,” Hagen says. “The policy was particularly effective at lowering rates of deli meats and hot dogs.”

“The inter-agency risk assessment on Lm at retail delis…not only gives us a better understanding of this public health threat, it also describes a clear path forward,” Hagen says. “We can prevent illnesses and save lives by .....controlling temperatures in the deli case and putting in measures to prevent cross-contamination.....”

Major findings in the risk-assessment include at least nine of every 100 cases of listeriosis caused by contaminated deli products could be prevented if all refrigerated, ready-to-eat foods are stored at 41˚F or below. Ninety-six of every 100 cases of listeriosis caused by contaminated deli products could be prevented if all deli products that support Lm growth were reformulated to include a growth inhibitor. The study notes this benefit may be smaller, in part, because the amount of growth inhibitor used may not be effective throughout the shelf-life of a food, and it can affect the flavor.

Cross-contamination dramatically increases the predicted risk of listeriosis, the study states. Slicers are challening, but the risk assessment states proper cleaning and personal hygiene can make a difference.

Twenty-two of every 100 cases of listeriosis caused by contaminated deli products could be prevented if current levels of Lm in ready-to-eat foods received by the retail deli from processing establishments were reduced by half. The study suggests that continued efforts to prevent low levels of Lm contamination during processing, even on products that do not support growth of the pathogen, reduces the risk from these products and other ready-to-eat foods that can be subsequently cross-contaminated in the retail delicatessens.

“From an FDA vantage point…the real takeaway for us and our understanding is just what a dynamic problem this is,” says Michael Taylor, FDA Deputy Commissioner for Foods and Veterinary Medicine. “It’s not static. We’re seeing through the work of CDC and our experience investigating outbreaks, new food commodities we had not seen contaminated before being contaminated.”

“The basic phenomenon here is Lm is an environmental contaminant,” Taylor adds. “It’s present anywhere food is being prepared; foods that are vulnerable and support growth of Lm are vulnerable to contamination that can make people sick.”

Advances in genetic fingerprinting have helped public health agencies identify many outbreaks, Frieden says. More should be done to expand these technologies.

“We need to continue to expand the molecular technology and the tracking technologies that we have to identify the causes to figure out and then implement prevention strategies,” CDC’s Frieden says.

Testing, testing

Several high-profile foodborne illness outbreaks ushered in major reforms of federal food-safety laws. With new legislation came increasing regulatory pressure on food manufacturers to close gaps in their pathogen prevention and detection practices. The Food Safety Modernization Act in the United States and the Safe Food for Canadians Act in Canada places the onus of prevention on food manufacturers and gives the feds the power to police manufacturers more closely.

William Hogan, president and CEO of FoodChek Systems Inc., Calgary, Alberta, says more policing will mean more testing, which will propel the food-safety industry from a $2.5 billion industry to $5.5 billion by 2018.

Enter ‘rapid’ testing

St. Paul, Minn.-based 3M has been developing Listeria testing products since the 1980s, says Kevin Habas, 3M Food Safety Global Technical and Regulatory Affairs manager. It was around that time the company introduced its Listeria Visual Immunoassay test for the 3M Tecra technology. Since then, rapid test kits for Listeria and Lm have emerged as one of the fastest-growing industry segments.

“As global regulatory requirements have changed and become more stringent, the demand for Listeria testing, in particular, has dramatically increased,” Habas says. “And as the food industry and food-testing industry has become increasingly competitive, the drive to get faster, more detailed results has increased.”

3M offers a rapid test kit for Listeria under the company’s 3M Molecular Detection System, which includes assays for Listeria, Lm and other organisms. Released in July, the assay uses isothermal amplification of nucleic acid sequences, while bioluminescence detects the amplification. Presumptive positive results are delivered in real-time while negative results are displayed after the assay is completed. The technology can be applied to enriched foods and food process samples.

Life Technologies Corp. , Carlsbad, Calif., offers a line of Listeria testing solutions that detect Listeria spp. and/or Lm in food products and on environmental surfaces. The company says PCR-based (polymerase chain reaction) testing methods have created demand for fast and cost-effective sample preparation methods that can extract high-quality DNA from an array of sample types. PCR, sometimes called molecular photocopying, is a technique used to amplify or copy small segments of DNA.

“With an increased emphasis on food environmental monitoring and increasing regulatory pressures for food companies to demonstrate management and reduction of food pathogens, demand for Listeria in product and environmental testing continues to grow,” says Ravindra Ramadhar, business director, Food Safety for Life Technologies.

Speed is critical

When 3M set out to develop its Molecular Detection System, which includes a Listeria assay, company representatives met with customers throughout the world. A few themes emerged from these conversations, Habas says.

“First of all, the time-to-result [TTR] that testing technologies can offer food processors is critical, as customers look to identify Listeria as immediately as possible and minimize delays in their workflow,” he says. “The limit of detection that a technology offers and how sensitive it can confirm organisms like Listeria in food as well as food-processing environment-based samples, is also essential.

“Automation becomes important to those food-processing customers looking to eliminate transfer steps and reduce chances of human error that could compromise process flow andproduct quality,” Habas says.

FoodChek Systems offers Listeria spp. Environment Rapid Tests, which the company says are more sensitive than PCR systems. They can deliver accurate results in less than 24 hours, which includes enrichment time.

“We’re 50 times more sensitive and sensitivity is speed,” Hogan says. “We eliminate a full day from the process. Time is money.”

To address industry’s need for speed in testing, Life Technologies developed PrepSEQ Rapid Spin Sample Preparation Kits. It offers the quality and performance of high-throughput laboratories at a scale fit for low-to-medium throughput applications.

Life Technologies offers a solution that enables pooling of samples and then testing on a single platform.

“This provides the customer the ability to screen multiple samples faster with one assay, saving time and money,” Ramadhar says.

Food-safety culture

Communication is key when integrating a testing system into a company’s food-safety program. It’s important for the company to have a culture of food safety. Testing doesn’t replace basic food-safety protocols, but rapid testing can provide actionable results and can help companies to gain information on the effectiveness and potential break down in their controls, Ramadhar says.

“Through trending analysis, it can be a proactive, predictive approach to ensure the controls stated in a food-safety program are effective.”

“In addition to staying compliant with global regulatory standards, we always recommend customers conduct an internal validation of any of our pathogen detection tests on their foods and environments to confirm the test is optimally performing,” 3M’s Habas says. “Beyond that, there is nothing that should preclude them from adopting our pathogen detection technologies.”

FoodChek Systems’ Hogan says in the event of an incident, food companies must be able to show there were no patterns or trends of food-safety problems leading up to the incident.

“You have to do everything in your power to make sure you’re producing a high-quality, safe product,” says Hogan.