This backgrounder is written for consumers: To answer questions frequently asked about L. monocytogenes and the illness it causes, to describe public health and enforcement activities being conducted by the Federal government to control L. monocytogenes, and to outline precautions consumers and other food handlers can take to keep food safe and prevent listeriosis.
The Food and Drug Administration (FDA), the Food Safety and Inspection Service (FSIS) and the Centers for Disease Control (CDC) are working together to provide the public with this information. Pregnant women and immune-compromised consumers may also wish to contact their physicians with questions about listeriosis.
What is new is the recognition that L. monocytogenes bacteria may be spread in food. In earlier time, many believed farm animals transmitted L. monocytogenes to farm workers. But when listeriosis appeared in city dwellers, public health authorities realized that animal contact was not always the source of disease transmission.
It has been only in the past decade that researchers have recognized L. monocytogenes as an agent of foodborne illness. Fecal contamination is one way the organism is spread to raw agricultural products. For example, farm animals may pick it up from consuming improperly fermented silage, and then vegetables may become contaminated when animal manure carrying the organism is used for fertilizer. Animals in a herd also may pick up L. monocytogenes from other animals or manure containing the organism.
Discrepancies in information available on proper cooking prompted FSIS in 1988 to contract with a private laboratory to conduct research that has become the basis for FSIS regulations on proper cooking of roast beef. Earlier work focused on cooking temperatures and times needed to destroy Salmonella. The new study conducted by the laboratory looked at cooking temperatures and times that will destroy L. monocytogenes, and confirmed the adequacy of current regulatory cooking standards for eliminating the organism in FSIS-regulated products.
In addition, FDA researchers and FDA-funded research have confirmed the adequacy of commercial pasteurization for eliminating the organism in dairy products.
Post-processing contamination, rather than failure of heating or pasteurizing processes, is usually suspected when L. monocytogenes is detected on processed products.
FDA and FSIS developed culture procedures that rely on the presence of antibiotics in the medium, which allow multiplication of L. monocytogenes but inhibit multiplication of competing organisms. In 1986, independent laboratories verified the accuracy of the new FSIS method for meat and poultry. The FDA method has also been reviewed and accepted.
As more is learned about the bacteria and their control, new and even better tests are being developed. An example is FDA's gene- probe method.
Also, the scientific literature contains a few isolated reports of occupational listeriosis; for example, farm workers and veterinarians who work with animals have developed minor skin infections..
The highest incidence of listeriosis has been in persons over 60 years old and newborns. One third of infections occur during pregnancy and may lead to spontaneous abortions or serious illness in newborns. Others most at risk include patients with immune systems compromised by cancer, AIDS, or immunosuppressive medications such as steroids; and patients suffering from cirrhosis, diabetes and ulcerative colitis.
The more serious forms of listeriosis can result in meningitis (brain infections) and septicemia (bacteria in the bloodstream). Pregnant women may contract flu-like symptoms of listeriosis; complications can result in miscarriage, stillbirth, or septicemia or meningitis in the newborn. In older children and adults, complications usually involve the central nervous system and blood stream, but may include pneumonia and endocarditis (inflammation of the lining of the heart and valves). Skin contact with L. monocytogenes can cause localized abscesses or skin lesions.
It takes from one to six weeks for a serious case of listeriosis to develop, although flu-like symptoms may occur 12 hours after eating L. monocytogenes-contaminated food. Onset time probably depends on the health of the patient, the strain of L. monocytogenes and the dose--or amount of bacteria-- ingested.
From the 1986-1987 study results, as well as from findings in studies conducted form 1989-1990, CDC determined that sporadic (non-outbreak) individual cases of listeriosis were associated with soft cheese, undercooked poultry, hot dogs not thoroughly reheated and food purchased from delicatessen counters.
Thorough cooking will destroy L. monocytogenes on foods. Nonetheless, FDA and FSIS are committed to reducing contamination of raw foods by L. monocytogenes and other potentially harmful bacteria.
Surveillance data also indicate that about 425 deaths occur each year in the United States. The probability of death varies greatly depending on the patient's age and status of immune function. (See section on "Who is most at risk?") About 5 percent of the 9,000 food poisoning deaths each year are due to listeriosis.
Preliminary data suggest that the rate of listeriosis may have declined substantially during 1991 in several areas, perhaps related to intensified efforts to reduce Listeria contamination of foods.
Both agencies have testing programs for L. monocytogenes. The goals of these programs is to help government and industry identify the causes of contamination in processing plants and to make permanent changes that will reduce Listeria monocytogenes contamination, prevent problems and ensure a safe food supply. Both agencies can hold or detain products at the food processing plant, request a voluntary recall of the product or seize products through court order if necessary.
Initially, FSIS regulatory testing programs included selected cooked meat products. Following a CDC report that traced the first case of listerial meningitis to incompletely heated turkey franks consumed by a cancer patient, FSIS expanded the L. monocytogenes monitoring program to further prevent the sale of any cooked and ready-to-eat meat or poultry products from which L. monocytogenes is isolated, such as cooked sausages (including frankfurters and bologna), cooked roast beef, cooked corned beef, sliced canned ham, sliced canned luncheon meat, jerky, cooked poultry, and poultry and meat salads and spreads.
When ready-to-eat meat or poultry product is found to contain L. monocytogenes, the plant is notified and the product is subject to detention at the plant, voluntary recall or court- ordered seizure. From 1987 through March 1992, 27 FSIS-regulated cooked products from 27 firms have been recalled, including frankfurters, bologna and other luncheon meat, chicken salad, ham salad, sausages, chicken, sliced turkey breast and sliced roast beef.
FDA's monitoring programs initially concentrated on cheese and dairy products both domestic and imported. Later, FDA expanded coverage to include other ready-to-eat foods such as sandwiches, prepared salads and smoked fish. From 1987 to March 1992, 516 products from 105 firms have been recalled.
The agencies' stepped up monitoring and surveillance programs for L. monocytogenes, and food industry efforts have helped identify intervention measures aimed at controlling the organism.
In a HACCP, points at which food risks are more likely to be introduced are identified, and interventions are introduced where control is possible to reduce the potential for consumption of unsafe products. For instance, insufficient cooking or raw meat, poultry or milk may allow the survival of pathogenic bacteria and present a hazard. Therefore, the agencies require adequate cooking temperatures to destroy the bacteria.
Areas of concern in food processing plants include plant design and layout, equipment design, process control, personnel practices, cleaning and sanitizing procedures, and verification of pathogen control.
Much of the dairy industry has already instituted control measures, based on HACCP principles. Other FDA-regulated industries are following the lead. In 1987, meat companies began to modify production facilities, such as rearranging plant layout and making changes in equipment. An industry working group also developed recommendations for all meat companies based on what is learned, and developed a training video on employee practices and plant hygiene. The poultry industry also instituted improvements.
The food industry, FSIS and FDA have conducted workshops to develop recommendations for controlling risks at critical points. Government and industry, including food processors and grocers, are also working with retail establishments and hotels and other institutions to identify critical control points and interventions to address hazards.
The Centers for Disease Control, FDA, FSIS and the National Advisory Committee on Microbiological Criteria for Foods (which includes food scientists from federal health agencies, universities and private industry) have developed food handler advice for preventing listeriosis.
Although most people are at very low risk for listeriosis, the risk of listeriosis and other foodborne illnesses can be reduced by following these tips:
Persons at increased risk for listeriosis such as pregnant women, the elderly, and those with immunosuppressive conditions can decrease the risk by:
As part of this campaign, FSIS is working with the Administration on Aging to develop fact sheets for the elderly about foodborne illness. FSIS also is working with USDA's Food and Nutrition Service's Special Supplemental Program for Women, Infants, and Children (WIC) to distribute information through WIC clinics. In addition, FSIS distributes several publications that address the problem of listeriosis, especially for those in at-risk groups. These publications include:
FSIS Publications, USDA Room 1180, South Building Washington, DC 20250FDA is participating in educational campaigns and also distributes publications about L. monocytogenes. These include:
You can order copies from:
Food and Drug Administration
5600 Fishers Lane
Rockville, MD 20857*
In addition, for answers to your food safety questions, call USDA's Meat and Poultry Hotline at 1-800-535-4555. (In the Washington, DC area, call 202-720-3333.) Hotline hours are from 10 a.m. to 4 p.m., Eastern time.
FSIS
1-888-674-6854*
FDA
1-888-SAFEFOOD (1-888-723-3366)*
CDC
Media Inquires: 404-639-3286
Technical questions about listeriosis Meningitis and Special Pathogens Branch: 404-639-2215
Hypertext updated by ear/cjm 2004-JUL-16