Chuck Robinson of Produce Retailer writes the Listeria outbreak connected to caramel apples in late 2014 and early 2015 gave the produce industry a slap to remind it to remain vigilant about food safety.

Discussion of the outbreak dominated the first day of the seventh annual Center for Produce Safety Research Symposium on June 28-29.

That outbreak was traced to one apple supplier, Bidart Bros., Bakersfield, Calif. Only commercially produced, prepackaged whole caramel apples were involved.

There were 35 people from 12 states reported infected, according to the Centers for Disease Control and Prevention. Seven of them died before the case was closed, three of them linked to listeriosis.

Since the outbreak, the apple industry has changed focus from E. coli and compliance with Food Safety Modernization Act regulations to address listeria’s threat to the industry, said Ines Hanrahan, project manager for the Washington Tree Fruit Research Commission, Wenatchee.

In general, more attention to details is required to maintain sanitation, she said, including getting rid of standing water and daily cleaning zones that come into contact with food. Brushes need to be cleaned more frequently and dunk tanks must be cleaned and the water changed more often.

The stronger focus requires bigger cleaning crews and more time allotted to cleaning, she said. Training and rewards for improvement also are demanded.

“It’s about the people cleaning the brushes every day understanding why they are cleaning the brushes,” Hanrahan said.

The advent of whole genome sequencing, which provides more detailed and precise data for identifying outbreaks than the current standard technique, will mean more outbreaks will be detected, warned Martin Wiedmann, a food safety professor for Cornell University, Ithaca, N.Y. The produce industry must be prepared.

As the caramel apple-linked outbreak shows, the industry should realize what is happening in the field is of secondary importance, he said.

“I think we need to focus on our processing and packing facilities,” Wiedmann said.

There were many reasons at the outset of the investigation to not expect apples to be the outbreak source, said Kathleen Glass, associate director of the Food Research Institute at the University of Wisconsin-Madison. Reasons include the fact that the apples were sanitized and then dipped in hot caramel, which would seem likely to kill listeria. Also, the fruit is acidic, which would discourage listeria growth.

“You put all these factor together, and you don’t think apples are going to be a likely source of Listeria monocytogenes,” Glass said.”

However, the stems and calyxes of the fruit can harbor listeria, and pushing wooden stick through the calyx into the core also pushed listeria there.

“I’m really kind of surprised we hadn’t seen this sort of problem before,” Glass said.

Pat Kennelly, chief of the food safety section of the food and drug branch of California Department of Public Health, said problems were widespread at the Bidart Bros. packing facility. His staff’s investigation began well after the facility had closed operations for the season on Oct. 31.

“Given the level of contamination we found a month after operations had ceased, I can’t imagine what we would have found if we had tested when it was in operation,” Kennelly said.