Food Protection Connection: Powering Up Listeria Control

(reprinted from Dietary Manager, November/December 2009)

While foodborne illness case-counts are not as high as for Campylobacter, Salmonella, or E. coli, Listeria is a leading foodborne cause of hospitalization and death. About one in five victims dies from the illness, according to the CDC.

Symptoms of infection with Listeria include fever, muscle aches, and sometimes nausea or diarrhea. If it spreads into the nervous system, new symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur.

Highly Susceptible Populations

As with other foodborne illnesses, scientists can pinpoint groups who are at special risk of becoming ill and suffering serious consequences. For Listeria, pregnant women top the list. One-third of all Listeriosis cases afflict pregnant women, says the CDC, and for these women, the illness often travels to the baby. Miscarriage, stillbirth, premature delivery, or infection of the newborn are common.

Also at risk are the elderly, chronically ill patients, and those with suppressed immune systems (e.g., a person who has had an organ transplant). Medications that can increase risk of foodborne illness include gastric acid blockers (e.g., given to a person with peptic ulcer disease or gastroesophageal reflux disease), and immunosuppressive drugs (e.g., given to a person who has had an organ transplant). The accompanying Table summarizes those at risk.

• Pregnant Women
  During pregnancy, the immune system is weakened, which makes it hard for the mother’s body to fight off harmful foodborne bacteria. Hormonal changes during pregnancy have an effect on the mother’s immune system that lead to an increased susceptibility to Listeriosis in the mother.
• Unborn Babies and Newborns
  Harmful foodborne bacteria can cross the placenta and infect the developing fetus. The unborn baby and newborn don’t have a fully-developed immune system to fight off harmful foodborne bacteria.
• Older Adults
  Immune systems weaken as people age, which makes it harder for the body to fight off disease. Older adults often suffer from chronic health conditions, which make them more susceptible to foodborne illness. In addition, poor nutrition and poor blood circulation may result in a weakened immune system. Stomach acid also decreases as people get older, and stomach acid plays an important role in reducing the number of bacteria in our intestinal tracts—and the risk of illness.
• People with Weakened Immune Systems
  The immune systems of transplant patients and people with certain illnesses, such as clients with HIV/AIDS, cancer, diabetes, and kidney disease, are often weakened. Thus, their bodies are unable to effectively fight the harmful bacteria.

The Food Factor

Which foods require the most rigorous control to prevent Listeriosis? The most common culprits are cheeses made from unpasteurized milk, as well as processed meats, such as deli meats and hot dogs. High temperatures used during meat processing destroy the bacteria, but re-contamination in the manufacturing industry is a concern.

In the foodservice environment, processed meats require vigilant time and temperature control. Basically, the longer these products sit in the refrigerator—and the higher the refrigeration temperature—the more opportunity Listeria have to grow. This is why temperature checks on delivery, prompt storage, FIFO rotation, and observation of use-by or sell-by dates is imperative. Keeping the refrigerator cold (holding food at or below 41°F) is crucial, too. As these two factors combine to influence bacterial growth, time and temperature are key controls for the Listeria risk.

More controls recommended by the CDC and FDA focus on purchasing decisions and preventing cross contamination, e.g.:

• Avoid unpasteurized (raw) milk or foods made from unpasteurized milk, e.g. queso fresco.
• Avoid refrigerated smoked seafood, unless it is contained in a cooked dish, such as a casserole (a control suggested for highly susceptible populations).
• Avoid refrigerated pâtés or meat spreads (a control suggested for highly susceptible populations).
• Wash hands after handling hot dogs, luncheon meats, and deli meats.
• Wipe up refrigerator spills promptly so Listeria don’t have a place to grow.

Finally, endpoint cooking is a powerful control for processed meats. The USDA advises consumers, “Although hot dogs are fully cooked, those at increased risk of foodborne illness should reheat hot dogs and luncheon meat until steaming hot before eating, due to the threat of Listeriosis.” (USDA. Hot Dogs and Food Safety).

New research shows that microwaving is a highly effective cooking technique for making hot dogs safe. Patricia Kendall and colleagues tested various time and power combinations, as reported in the Sept. 2009 issue of Journal of Food Science. Their suggestion: Microwave hot dogs for 75 seconds at 1100 watts. Upon completion, the hot dogs should sit for two minutes to allow heat to travel to any cold spots. (Keep in mind that effectiveness of microwaving also depends on the amount of food you are cooking in a batch.) The researchers recommended that package labeling specify effective reheating techniques. They also noted, “Appropriate reheating recommendations for these products is critical,” with special emphasis on high-risk groups such as the elderly.

Because of its unique characteristics and grave risks, the Listeria threat merits special attention from dietary managers and foodservice teams, especially those charged with protecting vulnerable seniors. Attention to menu planning, purchasing, storage, handwashing, prevention of cross contamination, and endpoint cooking can go a long way in ensuring the well-being of your residents.

by Sue Grossbauer, RD
Sue Grossbauer, RD, is DMA's webmaster, author of several books, and a regular contributor to DIETARY MANAGER magazine.