October 22, 2008
Because Listeria is commonly found in the environment, it is likely that future outbreaks of listeriosis will occur. Indeed, a separate outbreak of Listeria recently occurred in Quebec as a result of contaminated cheese. So far, 31 people have developed listeriosis from this second outbreak, one of whom has died.
CATIE previously published Listeria risk-reduction tips provided by Health Canada at: www.catie.ca/catienews.nsf/CATIE-NEWS.
Now here is more background information about Listeria and listeriosis and HIV.
Listeria is commonly found just about everywhere -- in soil, water, animals, decaying plants. Very small amounts of these bacteria are found living harmlessly in the intestines of some people.
Listeria can grow at temperatures commonly found in refrigerators, between 4° and 10°C. The lower the temperature, the harder it is for Listeria to grow. Health Canada recommends that refrigerator temperature be kept around 4°C. Freezing food generally does not kill these bacteria. Steaming or boiling food is an effective way to kill Listeria.
Listeriosis was first conclusively linked to eating contaminated food because of an outbreak of this illness in Atlantic Canada in the early 1980s. Researchers zeroed in on pre-packaged coleslaw. Their investigation revealed that the cabbage used to make the coleslaw was likely contaminated due to exposure to sheep manure that contained Listeria. Because cabbages are often stored over winter, this prolonged storage allowed Listeria to multiply, reaching high levels that could easily cause disease.
Since that time, researchers have learnt much about Listeria and expanded the list of foods that could become contaminated with this germ, as follows:
Researchers at the U.S. Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) reviewed many reports of Listeria outbreaks that have occurred in high-income countries. They assessed the different types of food linked to the outbreaks and their potential to be contaminated with Listeria. Health Canada's recommendations for safer eating are identical.
Here are some foods that are at generally moderate-to-high risk for Listeria contamination:
For more details about Health Canada's tips on safer eating for people with weakened immunity, see the September 18, 2008 issue of CATIE News at: www.catie.ca/catienews.nsf/CATIE-NEWS.
Bear in mind that foods contaminated with Listeria do not necessarily smell as though they are spoiled.
Listeria bacteria can disease -- listeriosis -- and even life-threatening complications in people with weakened immunity. Unfortunately, the symptoms of listeriosis are very general and can develop any time between two and 70 days after eating contaminated food. Initial symptoms of infection may include the following:
For the most part, healthy adults and children who eat Listeria-contaminated food will develop mild or moderate symptoms of listeriosis. However, people with weakened immune systems are at high risk for developing listeriosis and can develop additional complications, including the following:
People at high risk of developing listeriosis include the following:
Researchers at the University of California at Los Angeles (UCLA) recently reviewed details on about 1,200 Listeria-related deaths in the U.S. that occurred between 1995 and 2005.
They found that the average age at the time of death was 68 years. The people who were 85 years or older were at greatest risk of death.
Because the use of highly active antiretroviral therapy (HAART) can partially restore the immune systems of HIV positive people, the UCLA team also looked at deaths that occurred before and after 1996, the year HAART was introduced in many high-income countries.
The UCLA research team noted that before 1996 about 5% of Listeria-related deaths occurred in HIV positive people in the United States. After that year, about 3% of Listeria-related deaths occurred in people with HIV. Although this decrease was not statistically significant, the UCLA team suspects that Listeria-related deaths are now less common because of the widespread availability and use of HAART.
Still, listeriosis is uncommon in HIV-positive people in high-income countries but researchers are not sure exactly why this is the case. Indeed, none of the people affected by Canada's recent Listeria outbreak have been HIV positive. One possible theory for this is that Listeria is controlled by cells of the immune system not seriously degraded by HIV. Another possibility is that antibiotics such as Bactrim/Septra (trimethoprim-sulfamethoxazole) commonly used by HIV positive people help kill Listeria.
In addition to the previous list of people at high risk of developing listeriosis, the UCLA team found additional risk groups, as follows:
Because Listeria can cause severe complications in people with weakened immunity, the diagnosis and prompt treatment of this infection is vital.
The Public Health Agency of Canada (PHAC) recommends that doctors perform detailed investigations in immune-suppressed people who are suspected of having eaten Listeria-contaminated food. Here are PHAC's suggestions:
Note that PHAC encourages combination antibiotic therapy with ampicillin and gentamicin for people with sepsis caused by Listeria.
Here are some ways of reducing everyone's risk for listeriosis by Dr. Robert Bortolussi, one of Canada's experts on this topic:
Here are some ways for people with HIV and other conditions that put them at high risk for listeriosis to reduce their chances of encountering Listeria:
For more information on Listeria, visit this helpful website: www.hc-sc.gc.ca/hl-vs/iyh-vsv/food-aliment/listeria-eng.php.
Warnings and food-product recalls provided by Canada's Food Inspection Agency may be found at: www.inspection.gc.ca/english/corpaffr/recarapp/recaltoce.shtml.