Oregon State Public Health Laboratory identified a cluster of five patients infected with Salmonella Enteritidis. The five patients were from four Oregon counties and had onsets of illness ranging from February to April, 2004. Further investigation would lead to documentation of at least 29 patients in 12 states and Canada with matching SE isolates, since at least as far back as September, 2003.

After a thorough investigation by local, state, and federal officials, the illnesses were definitively linked to raw almonds distributed by Paramount Farms. The investigation led to the recall of roughly 18 million pounds of Paramount Farms raw almonds. The five Oregon patients were interviewed. All reported consuming Kirkland Signature brand raw almonds, purchased at Costco stores, and produced and distributed by Paramount Farms.

Interviews with the subsequently identified persons with matching SE isolates further confirmed the link to Paramount Farms. In addition, an environmental investigation revealed Salmonella to be present at Paramount from three samples from two-huller-shellers that supplied Paramount during the period of interest.