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Press Release

Update: Listeriosis Outbreak Investigation

Update October 1, 2002
Contact: CDC, Media Relations
(404) 639−3286

CDC and state health departments are investigating an outbreak of Listeria infections. Thus far, Listeria bacteria isolated from 36 patients have been shown to have matching DNA patterns; this strongly suggests that these patients acquired illness from the same food. These 36 patients live in Pennsylvania (14 cases), New York City (11 cases), New York State (3 cases), New Jersey (4 cases) Maryland (2 cases), Connecticut (1 case), and Michigan (1 case). All patients were hospitalized. Six persons have died. (2 in Pennsylvania, 2 in New York City, 1 in New York state and 1 in Michigan). Additionally, two miscarriages or stillbirths have occurred in New Jersey. These illnesses began occurring this summer, and have continued through September. Federal and state investigators are working to determine the source of infection.

In addition to the 36 patients whose illnesses have been confirmed as part of the outbreak, CDC and State Health Departments have learned about other cases of Listeria infection in the same region. DNA subtyping has shown that strains from 30 patients in these same states are different from the outbreak strain; these illnesses are part of the “background” of sporadic Listeria infections and are likely due to a variety of different foods. Testing of Listeria strains from more than 15 persons is ongoing; some of these will likely be the outbreak strain and some will not.

Listeriosis is a rare and often serious illness. About 2500 cases occur each year in the United States. The initial symptoms are often fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea or diarrhea. The illness may be mild and ill persons sometimes describe their illness as flu-like. If infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur. Most cases of listeriosis and most deaths occur in adults with weakened immune systems, the elderly, pregnant women, and newborns. However, infections can occur in otherwise healthy persons. Infections during pregnancy can lead to miscarriages, stillbirths, and infection of newborn infants.

Previous outbreaks of listeriosis have been linked to a variety of foods, especially processed meats (such as hot dogs, deli meats, and pate) and dairy products (such as soft cheeses and milk). Pasteurization eliminates Listeria bacteria; dairy products cause illness only when pasteurization is not done, is inadequate, or when food is contaminated after pasteurization. Investigation is ongoing to determine the food product causing the current outbreak.

Recommendations for persons at high risk, such as persons with weakened immune systems, the elderly, and pregnant women, and for other persons who want to decrease their risk of listeriosis, are the following:

  • Avoid foods from deli counters or thoroughly heat deli meat products before eating.
  • Heat hot dogs until steaming before eating. Avoid cross-contaminating other foods, utensils, and food preparation surfaces with fluid from hot dog packages, and wash hands after handling hot dogs.
  • Avoid soft cheeses such as feta, Brie, Camembert, blue-veined, and Mexican-style cheese. (Hard cheeses, processed cheeses, cream cheese, cottage cheese, and yogurt need not be avoided.)

The following food safety measures, which should be routine for all persons, can also reduce the risk of listeriosis:

  • Thoroughly cook raw food from animal sources, such as beef, pork, or poultry.
  • Wash raw vegetables thoroughly before eating.
  • Keep uncooked meats separate from vegetables and from cooked foods.
  • Avoid raw (unpasteurized) milk or foods made from raw milk.
  • Wash hands, knives, and cutting boards after handling uncooked foods.

If you have questions about Listeria, you can call your local or state health department, your physician, or visit the CDC web site at

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This page last updated October 1, 2002

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