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Listeria monocytogenes


Photo:Listeria monocytogenes

Listeria monocytogenes is present inside various animals including a broad range of livestock, fowl, wild animals, and fish, and commonly found in rivers, sewers, and feedstuff.  A variety of foods are subject to contamination, with milk, meat, and other animal foods at higher risk.  The growth range temperatures for these bacteria is wide (-0.4 to 45° C, with the optimum growth temperature of 37° C) and they can multiply even under low or cold temperatures.  Additionally, they can grow in salt concentrations as high as around 10%.

Although the sources and routes of infection are not clearly known, many cases of listeriosis found in contaminated foods have been reported in some foreign countries.  At the highest risk are pregnant women, unborn children, newborn infants, infants, elderly people, and persons with underlying medical problems.  Listeriosis infection may cause meningitis, septicemia, and miscarriages.  At risk persons should avoid eating and drinking such foods that are likely to cause infection.

Which foods can cause listeriosis?

Listeriosis can be caused by: milk, dairy products, (especially non-pasteurized dairy products), processed-meat foods (deli meats, or hot dogs), salads, processed-fish foods, and similar foods.  Additionally, various foods, especially pre-cooked “ready-to-eat” foods that are consumed without heating, such as, cooked foods sold in disposable containers, can cause listeriosis.

What are the symptoms of listeriosis?

The incubation period is as wide as 24 hours to three months.  In some cases, listeriosis can cause infections in the central nerve system including meningitis or bacillemia (bacilli circulating in the blood), while in other cases they cause light symptoms similar to fever.  Many healthy adults show no symptoms however, pregnant women, unborn children, newborn infants, infants, and elderly people, or persons with underlying medical problems (weak immune systems) are at higher risk of more severe complications such as: meningitis, septicemia (blood poisoning), or other conditions.

What are the key points to preventing listeria infection?

  1. Pregnant women, newborn infants, infants, and persons with underlying medical problems should avoid risky foods likely to cause infection (or vulnerable to contamination).
  2. Be cautious of foods processed for long-term preservation at a low temperature.
  3. Prevent secondary infections from foods that are likely to be contaminated.

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