On July 19, 2014, Wawona Packing Company voluntarily recalled certain lots of stone fruits, including whole peaches, nectarines, plums, and pluots, because of concern about contamination with Listeria monocytogenes. The recall was triggered by testing conducted by the company. On July 31, the recall was expanded to cover all fruit packed at the Wawona facility during June 1-July 17, 2014.

In early August 2014, results of testing by pulsed field gel electrophoresis (PFGE) of three isolates cultured from Wawona Packing stone fruit were uploaded to PulseNet, the national molecular subtyping network for foodborne disease surveillance. All three isolates were indistinguishable by two enzyme testing and assigned PulseNet pattern combination identification number “GX6A16.0139/GX6A12.0009.” A review of the PulseNet database identified four human isolates that were genetically indistinguishable to the subtype isolated in Wawona Packing stone fruit. Listeria monocytogenes was isolated in 3 patients (one each in Illinois, Massachusetts and South Carolina) between May 8 and July 8, 2014. The outbreak subtype of Listeria monocytogenes was isolated in a fourth patient, a Minnesota resident, on August 28. Whole genome sequencing (WGS) analysis by whole-genome multilocus sequence typing showed that isolates cultured from the Massachusetts and Minnesota patients were highly related (<10 allele differences and <10 high-quality single nucleotide polymorphism differences) to the isolates from recalled fruits, whereas the Illinois and South Carolina isolates were not. Furthermore, the epidemiologic data on these two patients did not support an association with stone fruit consumption. The South Carolina patient denied eating any fruit. Investigators were not able to contact and interview the patient in Illinois.

Public health investigators in Massachusetts and Minnesota administered a standardized Listeria Initiative exposure questionnaire to family members of each patient in their respective states. The Minnesota patient had consumed peaches from a store that received Wawona Packing stone fruit; however, the dates from receipts provided by the family indicated that the peaches were purchased after the recalled fruit was withdrawn from the market. After removal of the recalled fruit, the store had received Wawona Packing Company peaches that were not part of the recall as well as peaches from another California supplier.