MMWR reports today that on July 19, 2014, a packing company in California (company A) (a.k.a. Wawona Fruit) voluntarily recalled certain lots of stone fruits, including whole peaches, nectarines, plums, and pluots, because of concern about contamination with Listeria monocytogenes based on internal company testing. On July 31, the recall was expanded to cover all fruit packed at their facility during June 1–July 17.
After the initial recall, clinicians, state and local health departments, CDC, and the Food and Drug Administration (FDA) received many inquiries about listeriosis from concerned consumers, many of whom had received automated telephone calls informing them that they had purchased recalled fruit. During July 19–31, the CDC Listeria website received >500,000 page views, more than seven times the views received during the previous 52 weeks.
In early August 2014, a two-enzyme pulsed-field gel electrophoresis (PFGE) pattern shared by three L. monocytogenes isolates from stone fruit associated with the recall was uploaded to PulseNet. Four human isolates with isolation dates during the period May 8–July 8, 2014 (Illinois, Massachusetts, and South Carolina) and August 28 (Minnesota) were identified that had PFGE patterns indistinguishable from isolates from company A stone fruit. Samples of stone fruits from company A collected after the recall yielded an additional 31 L. monocytogenes isolates, 22 of which were indistinguishable from the initial isolates by PFGE; three other PFGE patterns were identified that did not match any isolates from clinical specimens collected during May 1–August 31. Whole-genome sequencing (WGS) analysis by whole-genome multilocus sequence typing showed that isolates from the Massachusetts and Minnesota patients were highly related to the isolates from recalled stone fruits, whereas the Illinois and South Carolina isolates were not.
Strong evidence linked the Massachusetts case to recalled stone fruit, including food exposure interviews, receipt and shopper card data, and WGS results showing very high genetic relatedness between the patient’s isolate and isolates from nectarines. Consumption data and WGS results suggest that stone fruit was also the likely source of L. monocytogenes infection in the Minnesota case; however, the later dates of illness onset and fruit purchase suggest that the patient consumed stone fruit that was not included in the recall.