For a while it seemed like the diarrhea-inducing parasite cyclospora was everywhere. Confirmed and suspected cases number more than 22,000 across 15 states, with 517 people requiring hospitalization. Two people in Michigan died. But now, with signs that the outbreak is slowing down, experts say lettuce is probably safe to eat again.
The reason? Most of the contaminated produce is no longer available.
Federal health authorities have linked the outbreak to iceberg lettuce sourced from central Mexico and distributed by Taylor Farms, including at Taco Bell restaurants. On July 17, Taylor Farms announced a recall of shredded iceberg lettuce and salad mixes with “best if used by” dates through August 3, advising consumers to immediately discard any of the affected products. Grocery stores and restaurants are responsible for removing recalled items.
“That product is off the market, so I think there’s absolutely lower risk for cyclospora in terms of eating lettuce,” says Kali Kniel, a professor of microbial food safety at the University of Delaware.
But that doesn’t mean consumers shouldn’t still be vigilant about what they’re eating. As of August 6, there are two additional clusters of cyclosporiasis that officials are investigating. While a source has not yet been identified, officials in North Carolina say the state is looking into parsley and cilantro. At the same time, an outbreak of salmonella tied to jalapeños has infected at least 345 people across 27 states. On Sunday, Taylor Fresh Foods, the parent company of Taylor Farms, issued a recall of jalapeños and products containing jalapeños, including salsa and guacamole.
Total cases of cyclosporiasis could continue ticking up for weeks because of the lag time between when a person is exposed and when symptoms emerge, as well as delays related to seeking care, getting tested, and linking cases to contaminated products. On average, people exposed to cyclospora start to feel sick seven days after exposure, but symptoms can take up to 14 days to appear. Given the seven-day average incubation period and the recall in mid-July, most exposures likely happened in June and the first half of July.
Of course, there’s a chance that some people were exposed to the parasite after the recall occurred if they unintentionally ate a contaminated product they had at home. But now that those “best by” dates have passed, the original affected salad products should be long gone from refrigerators.
In Michigan, which was hit hardest by the outbreak, the state has reported more than 12,000 cases since June. Typically, Michigan sees 40 to 50 cases of cyclosporiasis annually. However, new cases have been on a downward trajectory since late July. On August 6, the state’s health department said Michigan residents no longer need to avoid bagged salad mixes and may resume their usual food handling practices as new cyclosporiasis case reports and diarrhea-related emergency department visits are on the decline.
“As we are seeing fewer cases reported than previous weeks and fewer people reporting the onset of new symptoms, we have growing confidence that the outbreak is declining,” Laina Stebbins, a spokesperson for the Michigan Department of Health and Human Services, tells WIRED.
The state health department first identified lettuce and salad greens as a potential source of the outbreak on July 13 and advised consumers to purchase whole heads of lettuce rather than bagged products and to discard outer leaves and thoroughly wash inner leaves before eating. The cyclospora parasite clings to surfaces and crevices of raw produce and is resistant to common food sanitizers, making it tricky to get rid of.
Joseph Eisenberg, a professor of epidemiology at the University of Michigan School of Public Health, says the outbreak is a good reminder of how complex food systems can increase the risk of foodborne illness.
“It’s not like a local farm can’t wind up with contamination and contaminated produce, but the supply chain is so much simpler that you’ll find it out quickly and deal with it,” he says. With bagged salad mixes, there can be several varieties of produce that all come from different farms or suppliers. That makes tracing the source of an outbreak more difficult. It’s also why buying whole lettuce is a safer bet.
Brian Schaneberg, executive director of the Institute for Food Safety and Health at the Illinois Institute of Technology, says drought and global warming also play a role in cyclospora risk.
“If you’re getting into drought season and the water supply is becoming an issue, then you’re having to get another source that has potential contamination points,” he says. Contaminated irrigation water is thought to be the most likely vehicle for spreading cyclospora to fresh produce.
And while the risk of cyclospora may be dwindling, it’s still summer and that means foodborne illness in general is at its peak. Pathogens thrive in warm temperatures, and outdoor events where food is being served provide the perfect breeding ground for harmful microbes.
“There’s always risk with fresh produce,” Schaneberg says. “This is the time that pathogens like to proliferate.”
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