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BACKGROUND: Listeria monocytogenes (Lm)is estimated to be the third leading cause of death from foodborne disease in the United States. During November 2014–February 2015, U.S. Food and Drug Administration (FDA) Coordinated Outbreak Response and Evaluation (CORE) Network, Centers for Disease Control and Prevention (CDC), and state and local partners investigated a multistate outbreak of listeriosis in which epidemiologic information strongly suggested a link to commercially-produced, prepackaged caramel apples. A traceback investigation was performed to identify the source of contamination.
METHODS: A case was defined as listeriosis in a person with onset on or after October 1, 2014, with an Lmisolate that had an outbreak-associated pulsed field gel electrophoresis pattern (PFGE) and was highly related by whole genome sequencing (WGS). FDA, in collaboration with local district offices, used information reported by ill persons about specific brands of caramel apples consumed and locations of purchase to perform a traceback investigation and determine the source of contamination. Inspectors collected traceback and traceforward documentation, firm information, and environmental and product samples.
RESULTS: As of February 12, 2015, 35 cases were identified from 12 states, including 11 pregnancy-associated illnesses with one fetal loss. Seven deaths were reported. Traceback of caramel apples was completed for 11 case-patients. All 11 consumed caramel apples produced by one of four manufacturers, and further traceback of apple sources led to convergence at one apple grower/packer, Bidart Bros., located in Bakersfield, California. FDA and state partners collected 19 product and environmental samples during inspections of this apple packing facility and caramel apple manufacturers. Environmental samples from the Bidart Bros. facility, samples of apples grown by Bidart Bros., and an environmental sample from one caramel apple manufacturing facility yielded Lm. These strains were indistinguishable by PFGE from, and were highly related by WGS to, strains of Lmisolated from ill persons. During December 24–29, 2014, three caramel apple producers issued voluntary recalls, and on January 6, 2015, Bidart Bros. voluntarily recalled all Gala and Granny Smith apples from their 2014 growing season.
CONCLUSIONS: Epidemiologic, laboratory, and traceback evidence demonstrated that commercially produced, prepackaged caramel apples were the source of Lm infections in this outbreak. Traceback provided a critical component to the investigation in demonstrating whole apples produced by a single grower/packer were the contaminated ingredient. This is the first documented outbreak of listeriosis associated with apples, specifically caramel apples.