Salmonella enteritidis contamination of ice cream associated with a 1994 multistate outbreak

Nine ice cream sample containers, representing three production lots involved in a 1994 outbreak of salmonellosis, were obtained from the manufacturer's distribution warehouse and from consumers. Single 100-g samples from each container were tested initially, with analyses beginning seven weeks after the ice cream was produced. Quantitative salmonella analysis of these samples was performed 14 weeks after the production date using a three-replicate, three-dilution most probable number (MPN) procedure using 100-, 10-, and 1-g samples. The MPN/g estimates ranged from 0.004 to 0.46 Salmonella enteritidis per g with six of nine samples showing an MPN value of 0.093 S. enteritidis per g. The 95% confidence interval for S. enteritidis among these samples was < 0.001 to 2.4 cells/g. The 95% upper limit of S. enteritidis per g was 0.38 for five of six consumer samples. Based on this, the number of S. enteritidis cells per serving (65 g) was 25. Based on the consumption of a single sundae cone (73 g, prepackaged), which caused severe illness in an eight-year-old boy and moderate to mild illness in the adult parents, the infective dose would appear to be no more than 28 cells.