Listeria monocytogenes

This bacterium is found in soil, silage, and other environmental sources. L. monocytogenes is quite hardy and resists the deleterious effects of freezing, drying, and heat.

Listeriosis is diagnosed when the organism is isolated from blood, cerebrospinal fluid, or an otherwise normally sterile site (e.g. placenta, fetus).

The symptoms of listeriosis include septicemia, meningitis, encephalitis, and intrauterine or cervical infections in pregnant women, which may result in spontaneous abortion (2nd/3rd trimester) or stillbirth. Infections are usually preceded by influenza-like symptoms including persistent fever. Symptoms such as nausea, vomiting, and diarrhea may precede more serious forms of listeriosis or may be the only symptoms expressed.

The bacterium enters the host's white blood cells and becomes blood borne.. Its presence intracellularly in cells also permits access to the brain and probably transplacental migration to the fetus in pregnant women.

The severity of L. monocytogenes infectiousness depends on its ability to survive and multiply in phagocytic host cells.

Listeriosis is only positively diagnosed by culturing the organism from blood, cerebrospinal fluid, or stool (although the latter is difficult and of limited value).

It has been associated with such foods as raw milk, supposedly pasteurised fluid milk, cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, fermented raw-meat sausages, raw and cooked poultry, raw meats (all types), and raw and smoked fish. Because it can grow at temperatures as low as 3°C it may multiply in refrigerated foods.

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.

Those at risk for listeriosis include: pregnant women/fetus - perinatal and neonatal infections; persons immunocompromised (by corticosteroids, anticancer drugs, graft suppression therapy, AIDS; cancer patients - leukemic patients particularly); less frequently reported (- diabetic, cirrhotic, asthmatic, and ulcerative colitis patients); the elderly; and occasionally normal people--some reports suggest that normal, healthy people are at risk, although antacids or cimetidine may predispose.