Listeriosis

The Chief Medical Officer of Health wishes to advise the public of an increase in the number of reported cases of listeriosis. Since the fall of 1999, nine cases have been identified among residents of Manitoba, primarily within the city of Winnipeg. On average, about three to four cases of listeriosis are reported yearly in Manitoba.

Listeriosis is a rare severe illness caused by a bacterial infection, Listeria monocytogenes. Symptoms include fever, intense headache, nausea and vomiting often with signs of meningitis or encephalitis. Occasionally, inflammation of other organs and skin lesions develop. Shock and sometimes death may occur. Listeriosis occurs more often in newborns, the elderly and those who have weakened immune systems. These severe infections with Listeria monocytogenes are reported to public health.

In most healthy people, exposure to Listeria monocytogenes causes no symptoms. Some people may develop a gastrointestinal illness. Pregnant women, who themselves may not feel ill, can pass the infection to their fetuses which may lead to miscarriage or stillbirth.

Listeria monocytogenes is commonly found in the environment, particularly in soils, vegetation, livestock feed and the feces (bowel movements) of humans and animals.

Investigation of the first eight cases of listeriosis since the fall of 1999 did not confirm any specific food source for the illness. The most recent case of listeriosis is still under active investigation.

Although listeria could contaminate any food, pregnant women and people at higher risk may choose to avoid certain foods that have more frequently been associated with past outbreaks in North America such as unpasteurized dairy products, soft cheeses, unwashed raw vegetables, deli meats and hot dogs. Please see "The Facts about Listeriosis" below for more information.

Everyone can reduce the risk of listeriosis (and other foodborne infections) by routinely following good food handling practices such as:

• thoroughly cooking raw meats;
• washing raw vegetables and fruits before eating them;
• keeping uncooked meats separate from other ready-to-eat foods;
• avoiding unpasteurized milk;
• and washing hands, knives and cutting boards after handling uncooked foods.

For further information, contact:

Dr. Joel Kettner
Chief Medical Officer of Health
Manitoba Health
(204) 788-6666

or Dr. Sande Harlos
Medical Officer of Health

Winnipeg Region Health Authority
Contact via: Sherril Matthes
(204) 926-7009

THE FACTS ABOUT LISTERIOSIS

WHAT IS LISTERIOSIS?

Listeriosis is a rare severe illness caused by a bacterial infection, Listeria monocytogenes. Symptoms include fever, intense headache, nausea and vomiting often with signs of meningitis or encephalitis. Occasionally, inflammation of other organs and skin lesions develop. Shock and sometimes death may occur.

WHO GETS LISTERIOSIS?

Anyone can get the disease, but those at highest risk of severe illness are newborns, the elderly, persons with weakened immune systems and pregnant women.

WHEN DO LISTERIA INFECTIONS OCCUR?

Infections occur throughout the year. Although most cases occur sporadically, foodborne outbreaks do occur.

HOW IS LISTERIA SPREAD?

Listeria bacteria are widely distributed in nature and can be found in water, soil and vegetation. Infected animals may also serve as sources. Unlike other organisms, listeria can be spread by several different methods.

• Listeriosis cases in the past have usually been associated with:

• Unpasteurized dairy products and soft cheeses such as Brie or Mexican-style

• Raw fruits and vegetables and processed vegetables such as salad fixings, coleslaw, potato salad

• Ready to eat meats such as cold cuts and hotdogs, smoked fish & cooked seafoods.

Other meats such as ground beef, poultry and sausages may also be contaminated.

• In newborn infections, the organism may be transmitted from mother to fetus in utero, or directly to the fetus at the time of birth.
• Direct contact with the organism can cause lesions on the hands or arms.
• Person-to-person transmission can occur through sexual contact.
• Infection is also possible by inhaling the organism.

WHAT ARE THE SYMPTOMS OF LISTERIA INFECTION?

Since listeria can affect many different parts of the body, the symptoms vary. Healthy adults and children who are infected rarely become seriously ill. In most cases, listeria infection causes fever and gastrointestinal symptoms resembling many other mild illnesses. Sometimes, various types of sores at the site of infection are the primary symptom. In serious cases of listeriosis, this illness may lead to infections of the brain or blood, either of which can cause death, particularly in ‘at risk’ groups.

HOW SOON AFTER EXPOSURE DO SYMPTOMS APPEAR?

Listeriosis has an extremely variable incubation period. In large outbreaks, the range has extended from three to 70 days but is usually about three weeks.

HOW IS THIS DISEASE DIAGNOSED?

Specific laboratory tests are the only way to identify this disease. Since many cases may be mild, the disease may be more common than is realised.

ARE THERE SPECIAL RISKS FOR PREGNANT WOMEN?

Listeria infections are a significant risk for pregnant women, who themselves may not experience obvious symptoms. However, infection of the fetus can cause miscarriage as early as the second month of pregnancy, but more often in the fifth and six months. An infection later in pregnancy may cause stillbirths or lead to exposure during birth, sometimes resulting in infection of the newborn that may be fatal.

DOES PAST INFECTION WITH LISTERIA MAKE A PERSON IMMUNE?

There is little evidence of protective immunity even after a previous severe infection.

WHAT IS THE TREATMENT FOR LISTERIA INFECTION?

Several antibiotics are effective against this organism. Ampicillin, either alone or in combination with other antibiotics, is frequently used.

WHAT CAN BE DONE TO PREVENT THE SPREAD OF THIS DISEASE?

• Since the organism is widespread in nature, basic food handling and hygiene measures such as using only pasteurised dairy products, washing raw vegetables before eating them, eating well cooked meats and washing hands thoroughly before preparing foods offer the best protection.
• Those at high risk, such as pregnant women and persons with weakened immune systems may wish to avoid such foods as soft cheeses, uncooked hot dogs and food from deli counters, or may choose to thoroughly reheat cold cuts before eating.
• Listeria bacteria will grow slowly even at refrigeration temperatures so people at risk should not keep food in the refrigerator for more than seven days.

WHERE CAN I GET FURTHER INFORMATION?

Contact your local public health office or call Health Links at 1-888-315-9257 or 204-788-8200.