The Cantaloupe Crisis: What’s Next?

Wilson added that Costco is evaluating intervention strategies. “For example, we have some companies looking at steam pasteurization, surface pasteurization of the cantaloupe. That seems to work really well.” It’s an approach that’s been employed with beef carcasses ever since 1993’s deadly outbreak of E. coli in the Western states, in which four children died after eating tainted meat from Jack in the Box restaurants. Wilson, then in charge of special projects at Frigoscandia Equipment in Bellevue, Wash., worked with colleagues there to develop the steam pasteurization process.

“When we were doing the beef studies, we also tested cantaloupe,” he said, noting that the Jack in the Box outbreak occurred just two years after the Salmonella outbreak in cantaloupe. “By using steam at atmosphere, it turns to water when it goes through phase change on the surface of the cantaloupe, and it kills the bugs there. It’s pretty straightforward and efficacious, and I don’t really have an answer as to why it hasn’t been used widely in cantaloupe before. Right now, we have some pilots going on and it’s under serious review.”

Companies are also re-evaluating washing systems and what’s being used to wash the fruit. “Are they using surfactants, natural acids, or chlorine only?” Wilson asked. “And with all these intervention strategies, we also need to have something in place to prove they work. We’re asking vendors to work with us on that, and we’re getting a great response.”

But California’s Patricio said that a less-is-more approach to cleaning cantaloupes may be the best way to go—at least when it comes to melons grown in the specific growing conditions of his state—based on research conducted with the University of California-Davis in the wake of the 1991 outbreak.

“We did six years of sampling, and after that, we weren’t finding contamination even in greater risk areas, such as downwind of dairies and near corrals,” said Patricio. (The program looked for Salmonella and E. coli only—Listeria wasn’t a recognized issue at the time.) “Scientists concluded that the high heat, low humidity, and other climatic conditions in central California prevented the development and spread of those common bacteria in normal practice.”

So the researchers turned to industry cleaning practices. “At the time, there were probably 30-some shippers in California, with a dozen different techniques being used to prevent the spread of pathogens. We had elaborate wash systems, hydrocooling, deep cold and hot, hot, hot temperature—all sorts of things were being done to reduce risk,” said Patricio.

The scientists evaluated them all and concluded that most of them risked causing more contamination than they prevented. “They concluded that cantaloupes run more risk of contamination the more times they come in contact with people or common surfaces,” Patricio explained. “You want to limit human contact and get them as they are in nature as quickly as possible into a sealed container. This was a bit dismaying to those of us who had invested in elaborate systems, but field packing quickly became the norm.”

Patricio said that uncut cantaloupe with a whole, unbreached rind has a natural barrier against pathogens. “Years and years of research indicates that the rind and the biology of the melon prevent cantaloupe from uptaking bacteria into the edible portion. The best thing you can do is touch them as little as possible.”

Test-and-hold programs aren’t well suited for a product like cantaloupe, Patricio said. “They have a 72 – to 96 – hour window. If I still have product 36 hours after I pack it, I’m in trouble,” he noted. “A cantaloupe has such a short shelf life that I’ve got to get it out of the field, packaged, pre-cooled, and shipped within 36 hours. But things like steam pasteurization and other new strategies have good potential going forward.”