Resumen: The incidence of human listeriosis in Navarra (Spain) was monitored during two different periods of time (1995-2005 and 2006-2011) by active surveillance in collaboration with the main hospitals within this region. A total of 72 cases of invasive listeriosis were detected, with an average incidence rate of 0.75/100,000 inhabitants. The incident rate shows a tendency to increase, as the first period (40 cases within 11 years) showed a rate of 0.65/100,000 while the second period (32 cases within 6 years) showed a rate of 0.86/100,000. Over the whole period studied, 44.4% of the cases were diagnosed among aged population (32 cases out 72), the group most affected by listeriosis, while case fatality (including fetal death) was 57.9% in pregnant women (n=11 out of 19 pregnancy-associated cases). Most of the isolated strains belonged to serotype
4b (n=38 out of 65 strains; 58.5%), but a significant increase of 1/2a serotype has been observed in recent years (P¿0.05). In addition, serotype 1/2c was isolated from a clinical case, and to the best of our knowledge, it is the first clinical isolation of this serotype in the region. In this chapter, the epidemiology of human listeriosis and how to improve the current Spanish surveillance system will be discussed.