Deli Items May Dish Up Dose Of Listeria

by Food and Drug Administration (FDA)

Some types of soft cheese, undercooked poultry, hot dogs not thoroughly reheated, food purchased from delicatessen counters, and other ready-to-eat foods are responsible for sporadic cases of listeriosis, mostly in pregnant women and people with suppressed immunity. The cases were identified by studies funded by the Food and Drug Administration and carried out by the national Centers for Disease Control from 1986 to 1990.

The cheeses found to contain the organism that causes the illness were mostly soft, white, Mexican style (such as Queso Blanco and Queso Fresco). Past studies have implicated feta, Brie, Camembert, and blue-veined cheeses such as Roquefort. No problems have been found with hard cheeses, processed slices, cottage cheese, or yogurt.

Listeriosis is a food-borne illness that may cause few or no symptoms in healthy people but can cause serious illness in people with suppressed immune systems and the elderly. It can also harm the fetus and cause illness in newborns.

The illness is caused in humans by one species in a group of bacteria called Listeria. The name of this species is Listeria monocytogenes, which is often shortened, in common parlance, to "Listeria."

CDC had previously identified several outbreaks of listeriosis. But since most cases occur sporadically, research was needed to find out more about the role played by various foods.

The latest CDC study results were published in the April 15, 1992, Journal of the American Medical Association. CDC researchers confirmed 301 cases of listeriosis from November 1988 through December 1990 in California, Tennessee, Georgia, and Oklahoma. Though the rate of infection was low for the total population (7.4 cases per million), 23 percent of the infections were fatal.

Susceptibility and Symptoms

People most commonly contract listeriosis by eating food contaminated with the organisms, although 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). (See accompanying article, "Old, Tough Germ.")

Newborns and people over 60 have the highest incidence of listeriosis. One-third of infections occur during pregnancy and may lead to spontaneous abortion or serious illness in the newborn. 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 symptoms vary, depending on the individual's immune resistance. Symptoms may be limited to fever, fatigue, nausea, vomiting, and diarrhea, or these symptoms can progress to a more serious illness.

The more serious forms of listeriosis can result in meningitis (brain infection) and septicemia (bacteria in the bloodstream). Pregnant women may develop flu-like symptoms with complications resulting in miscarriage, stillbirth, or septicemia or meningitis in the newborn. In older children and adults, complications usually involve the central nervous system and bloodstream, 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 patient's health, the strain of L. monocytogenes, and the dose — or amount of bacteria — ingested.

Outbreaks

Four reported outbreaks of listeriosis in North America in the past decade are either known or suspected to have been caused by L. monocytogenes in food.

An outbreak in 1981 in Nova Scotia resulted in 41 cases of listeriosis, including 18 deaths; 83 percent of the cases were perinatal (occurring in infants near the time of birth). The outbreak was traced to L. monocytogenes on coleslaw that had been made from cabbage grown in a field fertilized with manure from Listeria-infected sheep.

An outbreak in 1983 in Boston resulted in 49 cases of listeriosis, including 14 deaths; 14 percent were perinatal, the rest were adults with lowered immunity. Although pasteurized milk from Listeria-infected dairy cows was linked to the outbreak, L. monocytogenes was not found in the suspected brand of milk.

An outbreak in 1985 in Los Angeles resulted in 142 cases of listeriosis, including 46 deaths; 85 percent were perinatal. The outbreak was traced to L. monocytogenes on soft, Mexican-style cheese manufactured with contaminated milk.

An outbreak in Philadelphia in 1987 resulted in at least 32 cases of listeriosis, including 11 deaths. The source was never identified.

Researchers are not sure how many L. monocytogenes organisms it takes to cause illness. The infective "dose" varies, depending on the susceptibility of the individual. However, it is noteworthy that four of the ill persons in the Los Angeles outbreak reported eating the implicated product (highly contaminated soft cheese) only once.

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