A number of acquired risk factors for listeriosis have been identified, such as pregnancy, age, cirrhosis, renal insufficiency, diabetes, cancer, HIV infection, transplantation and immunosuppressive therapies. If listeriosis is rare, the exposure to Lm is universal. The high prevalence of known risk factors in the general population and the low occurrence of the disease suggest that unknown parameters, such as host genetic factors, contribute to the susceptibility to listeriosis. This is supported by animal studies, which have shown that genes involved in innate and cell-based immunity are critical to control listeriosis. However, no genetic study on host susceptibility to listeriosis in humans has been performed so far, in the absence of prospective collection of patients' samples.