Purpose: This outbreak investigation demonstrates the effective use of traceback and environmental investigations to confirm the source of a SalmonellaEnteritidis outbreak associated with a free-range egg facility.
Methods: MDH epidemiologists interviewed all Salmonella Enteritidis cases that matched by pulsed-field gel electrophoresis (PFGE). Eight individuals infected with the outbreak strain of SalmonellaEnteritidis were identified in Minnesota with illness onsets in August and September 2011. Consumption of organic eggs from a common farm was statistically implicated in a case-control study. Five cases had specific egg purchase or consumption information that MDA investigators used to trace the eggs back to a common farm.
Results: The five cases of illness traced by MDA had purchased eggs from six different retail locations. All six retail locations received product directly from one egg laying facility in Minnesota. An on-farm traceback investigation found the farm used eggs from its own hens and eggs from nine other laying facilities in Minnesota to fill orders. A review of the production records indicated that only eggs from the implicated farm were associated case exposures. Twenty-four environmental samples were collected from the laying barn and candling room. Two samples collected from the egg belt were positive for the outbreak strain.
Significance: With the impending implementation of the FDA’s Egg Rule for small egg producers, this outbreak highlights the challenges associated with free-range organic egg production and some potential issues for producers in complying with the new regulations.