Salmonella enterica serotype Enteritidis and eggs: a national epidemic in the United States.

Beginning in the 1970s, the incidence of Salmonella enterica serotype Enteritidis (SE) infection and the number of related outbreaks in the United States has increased dramatically. By 1994, SE was the most commonly reported Salmonella serotype, with an incidence of >10 laboratory-confirmed infections per 100,000 population in the Northeast. Intensive epidemiologic and laboratory investigations identified shell eggs as the major vehicle for SE infection in humans, and that the eggs had been internally contaminated by transovarian transmission of SE in the laying hen. Three key interventions aimed at preventing the contamination and growth of SE in eggs have included farm-based programs to prevent SE from being introduced into egg-laying flocks, early and sustained refrigeration of shell eggs, and education of consumers and food workers about the risk of consuming raw or undercooked eggs. Since 1996, the incidence of SE infection in humans has decreased greatly, although many cases and outbreaks due to SE contaminated eggs continue to occur.