Listeria is a gram-positive rod-shaped bacterium that can grow under either anaerobic (without oxygen) or aerobic (with oxygen) conditions. Of the six species of Listeria, only L. monocytogenes causes disease in humans. Called an “opportunistic pathogen,” Listeria is noted to cause an estimated 2,600 cases per year of severe invasive illness. Perhaps not surprisingly then, “foodborne illness caused by Listeria monocytogenes has raised significant public health concern in the United States, Europe, and other areas of the world.” Given its widespread presence in the environment and food supply, the ingestion of Listeria has been described as an “exceedingly common occurrence.”
According to the CDC and other public health organizations, individuals at increased risk for being infected and becoming seriously ill with Listeria include the following groups:
- Pregnant women: They are about 20 times more likely than other healthy adults to get listeriosis. About one-third of listeriosis cases happen during pregnancy
- Newborns: Newborns rather than the pregnant women themselves suffer the serious effects of infection in pregnancy
- Persons with weakened immune systems
- Persons with cancer, diabetes, or kidney disease
- Persons with AIDS: They are almost 300 times more likely to get listeriosis than people with normal immune systems
- Persons who take glucocorticosteroid medications (such as cortisone)
- The elderly