Listeriosis refers to the invasive form of illness caused by the bacterium called Listeria monocytogenes. This form of the illness is the more severe of two types of illnesses caused by this organism.
The milder form presents with typical gastroenteritis symptoms, called “febrile gastro-enteritis” i.e. fever and diarrhoea. This latter form is usually not serious and most people heal quickly. However, the invasive form is far more serious causing 20-25% mortality (deaths). The invasive form is the one to be concerned about as the bacterium leaves the intestines and enters the blood, liver and cerebro-spinal fluid.
The illness listeriosis is contracted when a person consumes food that is contaminated (infected) with sufficient levels of the organism Listeria monocytogenes. An illness that is transmitted via food in this way is commonly known as a “foodborne illness” and the causal organism as a “foodborne pathogen”. Unfortunately, one will not know if the food is contaminated as it appears, tastes and smells normal.
Symptoms usually appear from 1-4 weeks after eating food contaminated with Listeria monocytogenes. Some people have reported symptoms starting as early as 3 days and as late as 70 days after exposure.
Listeriosis is not transmitted from person to person (like influenza for instance), with the exception of pregnant woman to baby transmission via the placenta and the blood system.
There are persons who are at greater risk of contracting listeriosis. These are pregnant women, the elderly (over 65 years of age) and persons with weakened immune systems, for example, organ transplants patients, personswith HIV/AIDS, diabetes, cancer and other autoimmune diseases. Symptoms usually appear from 1-4 weeks after eating food contaminated with Listeria monocytogenes but symptoms can appear 70 days thereafter.