Reduction in the incidence of human listeriosis in the United States. Effectiveness of prevention efforts? The Listeriosis Study Group

Background. —Food-borne transmission is now recognized as a major cause of human listeriosis. Objective. —To assess the impact of prevention efforts, listeriosis rates before interventions were initiated in 1989 were compared with more recent rates (1990 through 1993). Design. —From 1989 through 1993, multistate, laboratory-based active surveillance was conducted to identify all cases in whichListeria monocytogeneswas isolated from cultures or ordinarily sterile sites in an aggregate population of more than 19 million. Setting. —All laboratories serving acute care hospitals in up to nine surveillance areas in the United States. Interventions. —In 1989, a well-publicized case report of listeriosis linked to processed poultry led US regulatory agencies to enforce aggressive food monitoring policies and prompted industry to invest in cleanup efforts. In May 1992, consumer guidelines for listeriosis prevention were disseminated. Outcome Measures. —Cases of perinatal and nonperinatal listeriosis. Results. —The rate of listeriosis decreased in all surveillance areas. Projection of these rates to the US population suggests an estimated 1965 cases and 481 deaths occurred in 1989 compared with an estimated 1092 cases and 248 deaths in 1993, a 44% and 48% reduction in illness and death, respectively. Among adults 50 years of age and older, rates declined from 16.2 per 1 million in 1989 to 10.2 per 1 million in 1993 (P=.02). Perinatal disease decreased from 17.4 cases per 100 000 births in 1989 to 8.6 cases per 100 000 births in 1993 (P=.003). Three serotypes (1/2a, 1/2b, and 4b) ofL monocytogenesaccounted for more than 96% of cases during each year of the study (1989 through 1993). Conclusions. —The incidence of listeriosis in study areas was substantially lower in 1993 than in 1989. The temporal association of this reduction with industry, regulatory, and educational efforts suggests these measures were effective. (JAMA. 1995;273:1118-1122)