Listeriosis in Norway 1977-2003

In Europe, the incidence of invasive listeriosis has increased substantially during the last decades. We here present data from 289 listeriosis cases reported in Norway during the period 1977-2003, of which 12 cases were associated with 2 outbreaks and 39 cases were pregnancy-related. Medical records were obtained from 209 cases with listeriosis reported in 1977-2000. While the incidence of pregnancy-related listeriosis has remained stable at an average rate of 34 per million pregnant women per y during the period, the incidence of sporadic, non-pregnancy-related cases has increased from 1.1 to 3.7 per million per y. The present Norwegian incidence of reported cases is lower than in Denmark, but the case fatality rate is higher, indicating a possible under-reporting of mild listeriosis cases in Norway. We discuss how preventive measures, case identification and surveillance may have influenced listeriosis incidence in Norway.