Listeria is the common name for the pathogenic or disease-causing bacterium known as Listeria monocytogenes.  It is a foodborne illness that when ingested causes an infection known as listeriosis (Cossart & Bierne, 2001).  Approximately 2,500 illnesses and 500 deaths are attributed to listeriosis in the United States annually (CDC, 2005).

Listeria is ubiquitous in the environment, and can be isolated from wild and domestic animals, birds, insects, soil, wastewater, and vegetation.  The bacterium easily comes into contact with farm animals as it has been found to be present in grazing areas, stale water, and poorly prepared animal feed.  In addition to being present in the environment, Listeria can live in the intestines of humans, animals and birds for long periods of time without causing infection.

Because Listeria is present in nearly every environment – including in some food processing facilities – numerous opportunities for contamination exist during the food production process (Cossart & Bierne, 2001).

Healthcare providers frequently overlook Listeria as a possible cause of illness due to its unusual growth capabilities.  First, laboratories sometimes have a difficult time growing Listeria.  When it is grown, Listeria can be confused with other less harmful contaminants and disregarded.  Second, while most bacteria grow poorly when temperatures fall below 40°F, Listeria survives at temperatures from below freezing to body temperature, and grows best at the 0°F to 50°F range, which includes the temperature range used for freezing and refrigeration.

Due to its unusual growth capabilities, Listeria may be transferred in common ready-to-eat foods that have been kept properly refrigerated.  Thus, Listeria presents many challenges because of its ability to grow in diverse environments.  These host factors, along with the amount of bacteria ingested and the virulence of the strain, determine the risk of disease.

Symptoms of Listeriosis

It is believed that the ingestion of fewer than 1,000 Listeria bacteria can cause human illness.  The incubation period (time between ingestion the onset of symptoms) for Listeria monocytogenes infection, known as listeriosis, ranges from three to seventy days, and averages 21 days (Bryan, 1999).

A person with listeriosis usually experiences fever, muscle aches, and gastrointestinal symptoms such as nausea or diarrhea.  Five days to three weeks after ingestion of the bacterium, Listeria can access all body areas, including the central nervous system, heart, and eyes (FDA/CFSAN, 2003). If the infection spreads to the nervous system, symptoms such as headache, stiff neck, loss of balance, confusion, obtundation, or convulsions can occur. With brain involvement, listeriosis may mimic a stroke.Continue Reading What is Listeria?