In May 2009, diarrhea and fever developed in 8 persons living in southwestern France one day after they ate a homemade tiramisu prepared with raw eggs. Fecal analysis was performed on samples from 5 of the 8 persons. French investigators also cultured a sample from the tiramisu. In medical laboratories, the isolation was performed by using standard procedures (i.e., use of conventional selective media). Isolation from the food sample was performed as required by the current International Organization for Standardization ISO 6579:2002 (i.e., by 2 selective enrichment media). All cultures yielded S. enterica subsp. enterica 4,5,12:–:–.

An investigation at the suspected layer farm was conducted and showed the presence of 11 nonmotile Salmonella spp. isolates (with the same antigenic formula) in dust and feces collected from laying-hen houses. The layer farm, located in northwestern France, is a major farm that produces >32,000,000 eggs per year. All 17 isolates (5 from humans, 1 from the tiramisu, and 11 from the laying hens) were pan-susceptible to all antimicrobial drugs tested.

The authors conclude in Emerging Infectious Diseases that the nonmotile S. enterica 4,5,12:–:– strain involved in this outbreak has been present in laying hens in France for the past decade. Despite continuous advances in food safety and disease surveillance, control, and prevention, atypical pathogenic Salmonella spp. strains that bypass existing procedures do emerge. Foodborne bacterial infections remain a major public health concern.

This food poisoning outbreak also highlighted the need for a second selective enrichment media for Salmonella spp. detection not based on the motility in complement to the modified semisolid Rappaport-Vassiladis medium recommended as a single medium by the European Directive.

Complete paper available at http://wwwnc.cdc.gov/eid/article/18/1/11-0450_article.htm.