While rarely diagnosed prior to 1960, more than 10,000 cases of listeriosis were recorded in the medical literature between 1960 and 1982, and thousands more have been reported annually world-wide. This widespread increase in reporting is most likely due to demographic trends and changes in food production, processing and storage, especially the extended cold food chain and the ability of Listeria monocytogenes to grow at low temperatures.
L. monocytogenes is a bacterium responsible for opportunistic infections, preferentially affecting individuals whose immune system is perturbed, including pregnant women, newborns, people over 65 years, immunocompromised patients, such as cancer victims, transplant recipients, people on hemodialysis and AIDS patients. Thus, the increasing lifespan and medical progress allowing immunodeficient individuals to survive, partially explains the increasing incidence of listeriosis. Moreover, L. monocytogenes is ubiquitous and can grow at temperatures as low as 0 degrees C. At this temperature growth is very slow. The expansion of the agro-food industry, the widespread use of systems of cold storage, and changes in consumers demands have led to a large increase in the pool of Listeria that can cause food-borne infections.