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 [Rocourt J., 1991. Human listeriosis, 1989. WHO/HPP/FOS/91.3,
World Health Organization, Geneva, Switzerland; Rocourt, J., Brosch, R., 1992. Human
listeriosis, 1990. WHO/HPP/FOS/92.3, World Health Organization, Geneva, Switzerland;
Rocourt, J., Jacquet, Ch., Bille, J., 1997. Human listeriosis, 1991/1992. WHO/FNU/FOS/97.1,
World Health Organization, Geneva, Switzerland]. 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 foodborne infections.