Listeriosis in the United States: 1980-1982.

The magnitude of the public health problem associated with Listeria monocytogenes in the United States has been unknown, and the route of transmission is largely undetermined. Investigations of recent outbreaks, however, have shown that the infection can be foodborne. We estimated the expected frequency of sporadic listeriosis based on hospital discharge data from the Professional Activity Study of the Commission on Professional and Hospital Activities for the years 1980 through 1982. The incidence of listeriosis was 3.6 per million population per year, with an estimated 800 cases occurring in the United States each year. Attack rates were highest in neonates and in those aged 70 years and older (568 and 11 per million population per year, respectively). Overall mortality was 19.1%, with mortality rates increasing with advancing age. We estimated that listeriosis accounts for at least 150 deaths in the United States per year (fetal mortality not included). Throughout the nation, no marked regional differences in the incidence of the disease were apparent. We were able to identify three time-space clusters, which suggests the possibility that a portion of sporadic cases may, in fact, be previously unrecognized common-source clusters.