The current outbreak:
Seventeen cases have been reported across Canada since June 1, 2008, including 3 deaths in Ontario. Two BC cases were diagnosed in Prince George and Fort St. John. Common source in this outbreak seems to be Maple Leaf (ML) meats, which are sold under various brand names. The list of recalled products is at www.inspection.gc.ca/english/corpaffr/recarapp/recaltoce.shtml. Fraser Health has worked to ensure that implicated products were removed from care facilities in the region.
Listeriosis, high risk groups and clinical manifestations
Healthy adults and children occasionally get Listeria infections from consuming contaminated food, but rarely become seriously ill. Those at higher risk of infection and serious illness are: the elderly (especially in this outbreak where cases have been found in hospitals and long term care facilities); pregnant women and their unborn babies; people taking immune-suppressing medication; people with weakened immune systems (with cancer, diabetes, kidney disease, HIV/AIDS).
Listeriosis usually begins with influenza-like symptoms, including persistent fever. Fever, myalgias, arthralgias, back pain and headache are not specific and are classic initial symptoms of both bacteremia and viremia. Listeriosis does not necessarily present with gastrointestinal symptoms such as nausea, vomiting, and diarrhea but these might also be the only symptoms expressed. Clinical manifestations include septicemia, meningitis, encephalitis, corneal ulcers, pneumonia, intrauterine and cervical infections, spontaneous abortion, stillbirth, premature labor and infection in the newborn. Listeria infection is not associated with congenital malformations. The overall mortality rate of invasive L monocytogenes infection is 20-30%. When listeric meningitis occurs, the overall mortality may be as high as 70%; from septicemia 50%, from perinatal/neonatal infections greater than 80%. In infections during pregnancy, the mother usually survives.
Diagnosis: preferred sites for isolation of Listeria are normally sterile sites (CSF, blood, amniotic fluid, gastric washings, etc). Some studies suggest that 1-10% of humans may be intestinal carriers of L. monocytogenes, with or without necessarily having any symptoms. Therefore stool culture is not relied upon for diagnosis of listeriosis disease.
Treatment
Listeriosis can be treated with antibiotics. When illness due to Listeria occurs during pregnancy, antibiotics given promptly to the pregnant woman can often prevent infection of the fetus or newborn. Babies with listeriosis receive the same antibiotics as adults, although a combination of antibiotics is often used until physicians are certain of the diagnosis. Even with prompt treatment, some infections result in death, especially in the elderly and those with other serious medical problems. Parenteral penicillin, ampicillin and trimethoprimsulfamethoxazole have been reported to be effective therapies. Consultation with an infectious disease specialist is recommended. Listeria is inherently resistant to cephalosporins, so in patients presenting with bacterial meningitis and in high risk groups for listeriosis, usual antibiotics PLUS ampicillin should be considered until Listeria is ruled out.
The organism and its transmission
Listeria monocytogenes is a Gram positive bacterium, motile by flagella. These bacteria are often found in the environment, particularly in soil, vegetation, and the feces of humans and animals. Transmission is mostly through contaminated food, like the ones investigated in this outbreak and others. Rare cases of nosocomial transmission have been reported. Person-to-person transmission is unlikely to occur; therefore, isolation precautions are not necessary.
Good food handling practices reduce the risk of listeriosis, such as:
Cooking raw foods of animal origin well;
Washing raw vegetables before eating;
Keeping uncooked meats separate from vegetables and other ready-to-eat foods;
Avoiding unpasteurized milk; and
Washing hands, knives and cutting boards after handling uncooked foods.
Listeria may grow slowly even at refrigeration temperatures, so people at risk should not keep food in the refrigerator for more than seven days.
In addition to the above precautions, people at risk should either avoid or cook well the following foods:
Soft cheeses such as Brie, Camembert, blue-veined, and Mexican style cheeses;
Deli meats;
Hot dogs; and
Raw seafood and smoked fish.
For more information:
www.bccdc.ca; The Public Health Agency of Canada , and the HealthFile.
Thank you for your attention to this emerging outbreak and its potential to cause cases in our region.
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