Salmonella enteritidis outbreak in a restaurant chain: the continuing challenges of prevention.

In 1990, a Salmonella enteritidis (SE) outbreak occurred in a restaurant chain in Pennsylvania. To determine its cause(s), we conducted a case-control study and a cohort study at one restaurant, and a survey of restaurants. Egg dishes were associated with illness (P = 0.03). Guests from one hotel eating at the restaurant had a diarrhoeal attack rate of 14%, 4.7-fold higher than among those not eating there (P = 0.04). There were no differences in egg handling between affected and unaffected restaurants. Eggs supplied to affected restaurants were medium grade AA eggs from a single farm, and were reportedly refrigerated during distribution. Human and hen SE isolates were phage type 8 and had similar plasmid profiles and antibiograms. We estimate the prevalence of infected eggs during the outbreak to be as high as 1 in 12. Typical restaurant egg-handling practices and refrigeration during distribution appear to be insufficient by themselves to prevent similar outbreaks.