Contamination of hot dogs and cold cuts by a sometimes deadly bacterium -- one that is little known by the public -- has led to an extraordinary series of recalls in recent months, as well as increased government action to detect the problem sooner and prevent it.
There had been few reports of contamination by the bacterium, Listeria monocytogenes, over the last six years. But it resurfaced in December, when 35 million pounds of hot dogs and processed luncheon meats were recalled following an outbreak of listeriosis. Nearly 100 people in 22 states became ill, and 20 deaths were reported
Already this year, the Department of Agriculture has announced eight recalls because of listeria, seven of processed meats and one of milk. By comparison, the December recall was one of only three announced by the federal agency in 1998, and two were announced in 1997.
Tips for Avoiding
Listeriosis InfectionsTo prevent against protect against listeriosis, the government advises consumers to thoroughly cook raw animal products; thoroughly wash all food that is to be eaten raw, like fruits and vegetables; keep foods to be eaten raw separate from uncooked meats; and wash hands, knives and cutting boards with hot soapy water.
Those most vulnerable to listeriosis are advised also to do the following:
• Avoid all soft cheeses, including feta, Camembert, brie and blue-veined cheeses like Roquefort.
• Cook hot dogs until the internal temperature reaches 165 degrees, by either steaming or frying. Cooking in a microwave oven is not recommended.
• Avoid deli meats like salami, corned beef, bologna and liverwurst unless they get additional cooking -- for example, a hot corned-beef sandwich.
Although no deaths have been linked to the recalls so far in 1999, the December outbreak "shook everyone up," said Dr. Kay Wachsmuth, deputy administrator for the office of public health and science in the Department of Agriculture's Food Safety and Inspection Service.
But no one is quite sure what to make of it. "We can't tell at this point if there is a resurgence," Dr. Wachsmuth said.
Listeria does not pose much danger to most people. But it is a serious threat to the elderly, to pregnant women, to fetuses and newborns, and to those whose immune systems are compromised.
Food-borne bacteria like salmonella, E. coli and listeria are common in raw food, but cooking kills them. Scientists don't yet understand how listeria got into the processed foods that have been recently recalled. Testing techniques vary even among government agencies, and scientists do not yet know what level of bacteria is harmful.
Since the outbreak in December -- which was linked to products made by Bil Mar Foods, a subsidiary of Sara Lee -- the Agriculture Department has been searching for the reasons listeria has surfaced again.
The agency has begun to focus on the long shelf lives of these ready-to-eat products as a factor. Shelf life -- the length of time after manufacture that a food can safely be sold -- has increased considerably in the last 10 years because of better plant sanitation. But unlike many other disease-causing bacteria, listeria does grow at refrigerator and freezer temperatures.
Some recent changes designed to track and control listeria are already in place. Others are under study:
• A new DNA test has been adopted that allows the federal government to quickly link cases across the United States to a single source of contamination.
• Federal and state agencies are working to improve coordination so that information can be transmitted more efficiently.
• Food processors must now hold more product, and for a longer time, if a sample tests positive for listeria, to prevent the distribution of potentially contaminated foods.
• Regulators are considering making microbial testing mandatory, and requiring warning labels on franks and cold cuts. They are also weighing a consumer education campaign to warn those at greatest risk.
• Processors are examining new techniques for sanitizing their facilities. Failures in sanitation may be at the heart of the outbreaks.
Shortage of Data Challenges Officials
But underneath this flurry of activity a basic problem remains: lack of sound scientific data.
"Listeria is a major challenge," said Dr. Michael Osterholm, the former state epidemiologist at the Minnesota Health Department. "Manufacturers and consumers are left not knowing" what the infectious dose is, whether one strain is more virulent than others and whether current microbial testing techniques are sensitive enough to find the bacteria at very low levels.
Listeria is widespread in the natural world, lurking in many species of animals, including household pets, as well as in ticks, soil, dust, streams and a wide variety of foods. Healthy people are usually not affected, or at worst, suffer a throat or intestinal infection with mild flulike symptoms. But full-blown listeriosis may cause meningitis and encephalitis among vulnerable groups.
The population that is at risk is growing, as the number of elderly increases along with the numbers of people with weakened immune systems like cancer and transplant patients and people with AIDS. Pregnant women are especially vulnerable, as are their unborn children; even a mild infection may result in miscarriage, stillbirth or life-threatening illness for a newborn.
Health officials are particularly concerned because the percentage of people who die from listeria is apparently much higher than it is from better-known but less lethal food-borne bacteria like salmonella, campylobacter and E. coli 0157:H7. In addition, the incubation period is much longer. Symptoms of listeriosis can take up to 70 days to appear.
Listeriosis can be treated successfully with antibiotics, but even with drug treatment the mortality rate is about 30 percent. Of the 20 deaths linked to the Bil Mar outbreak, six were miscarriages or stillbirths and most of the adults were over 60.
Until December, there was good reason to think that listeria was under control. The last outbreak of listeriosis occurred in 1994. Epidemiologists differentiate between outbreaks, when multiple illnesses can be attributed to a single source, and individual cases with no known links.
Campaigns Since 1985 to Overcome a Germ
That followed years of efforts by food processors and the government to eliminate the problem. Scientists began to focus on listeria in 1985, after an outbreak traced to Jalisco brand soft cheese caused 142 cases of listeriosis and more than 40 deaths. Food processors took steps to improve sanitation in their factories.
At the same time, the Agriculture Department adopted a tougher policy for listeria levels in processed meats: automatic recall if any listeria is found. Between 1989 and 1993 there was a 44 percent reduction in the cases of listeriosis. The incidence has remained constant since then, at about 1,100 cases a year.
No one is certain if the growing number of recalls since the Bil Mar outbreak is the result of an actual increase in listeria contamination, increased public awareness, or additional government surveillance and the introduction of a new surveillance system called FoodNet and a sophisticated detection system called Pulsenet.
Because of a recent increase in financing for food safety, the government has set up eight sites around the country for active surveillance of food-borne diseases. They make weekly reports to the federal Centers for Disease Control and Prevention, which can immediately alert health officials in all 50 states. In the past it often took weeks, sometimes months, for the CDC to learn about problems.
Federal officials are also trying to improve the links among themselves and with state officials. A food-safety task force, called the Foodborne Outbreak Response Coordinating Group, was set up two years ago to deal with emergencies and was used in the large outbreak of salmonella in cereal in 1998. Notification is now made electronically. "We are getting better," said Dr. Wachsmuth of the Agriculture Department.
Pulsenet, activated in 1998, allows scientists to fingerprint the DNA of bacteria. Dr. Wachsmuth said that without Pulsenet, the listeria outbreak in December might never have been linked to Bil Mar products.
Over 3,000 Tests Performed Every Year
Each year the agency performs about 3,500 microbial tests for listeria in meat-processing plants. Once there has been an outbreak, the number of tests increases.
Beyond the routine tests, some of the recalls have been the result of microbial testing by distributors and by the agency's compliance officers responding to consumer complaints. "Lots of folks hear there are lots of recalls, and it makes them nervous and we catch more," Dr. Wachsmuth said.
New rules on food samples that test positive for listeria have been in place since August and may have played a role in the higher-than-usual number of recalls. Processors are now required to hold the entire day's output from the production line where a positive sample was found. Previously the plant was required to hold only the production from two hours on either side of the positive sample.
The manufacturers, too, are trying to take corrective action. They are changing the flooring for better drainage, looking at the locations of the air-conditioning unit, separating raw production from processed products and scrutinizing the methods they use for cleaning.
"Eradication of listeria from the environment that could contaminate food might not be impossible," Dr. Wachsmuth said. "But I'm not aware of any silver bullet. They just have to do these sanitary operation procedures more rigorously, and you couple that with environmental testing to make sure you've eliminated the listeria."
The Agriculture Department is considering mandatory microbial testing of ready-to-eat products, a move vigorously opposed by the industry. Some plants already test the environment. If listeria is discovered, then products are sometimes tested, but those in the industry would rather not discuss specifics.
Fears of Liability Discourage Some Tests
An industry spokeswoman explained that most plants do not test for listeria, because of the Agriculture Department's zero tolerance level for the bacteria.
"The federal government is standing in the way of doing testing," said Jenny Scott, the senior food-safety program director of the National Food Processors Association. "The problem is the zero tolerance policy for listeria in ready-to-eat products. Because you can't have any listeria in a product, there is a potential legal and regulatory liability if you test the product and find listeria."
The Center for Science in the Public Interest, a public-health advocacy group in Washington, has asked the Agriculture Department to require testing of hot dogs, cold cuts, luncheon meats and other fully cooked meat and poultry products.
"Right now the industry is fighting mandatory testing for economic, not scientific reasons," said Caroline Smith DeWaal, the director of food safety for the center. "The industry is liable if anyone gets sick, regardless of whether they test or not. Testing would add an additional layer of protection."
There is also no consensus on what the tolerance level should be, because of a lack of data. No one knows what an infectious dose of listeria is, Dr. Wachsmuth said.
Dr. Bala Swaminathan, chief of the food-borne and diarrheal diseases laboratory section of the CDC, said: "For foods that are not to be cooked, I'm in favor of zero tolerance until we have a better idea of the infectious dose, and I think microbial testing should be done. We will never be able to define a single infectious dose for everyone."
A Need Cited for Changes in Methods
The Agriculture Department has also been looking very closely at the shelf life of ready-to-eat foods. As listeria levels in processed meats dropped because of increased sanitation, between 1989 and 1993, processors extended the sell-by and use-by dates on their products. Long shelf life may provide the opportunity for listeria to grow and reach levels that cause listeriosis, and some testing methods are not sensitive enough to detect very low levels of listeria.
"Regulatory testing misses about 25 percent of what might be there," said Dr. Catherine Donnelly, professor of nutrition and food science and a food microbiologist at the University of Vermont. Dr. Donnelly said that a newer test she uses has a 98 percent success rate. The USDA is looking at new testing methods.
Suggestions have also been made about the importance of notifying high-risk consumers with an education campaign and warning labels on ready-to-eat products.
While food processors generally oppose warning labels, there is agreement that, as Janet Riley of the American Meat Institute said, the public does not know much about listeria. "I don't think there is a strong awareness about risks," Ms. Riley said. "I was never provided with any of this information by my obstetrician."
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