A difficult-to-trace parasite, messaging missteps contribute to summer of overwhelming Cyclospora outbreaks

Even after people undergo testing for cyclosporiasis, it could take another seven to 10 days for their results. 

“By the time this whole chain of events occurs, it can easily be two and a half to three weeks or more from the time you were exposed,” Osterholm said. 

An information vacuum

Last week, the FDA announced a second outbreak affecting at least 72 people unrelated to the nine-state outbreak linked to Taylor Farm’s lettuce. The source and location of this outbreak remains unknown, causing even more confusion. 

“There’s a huge cluster of cases in North Carolina and the southeastern states, which may well represent the second outbreak that’s not associated with the lettuce,” Craig Hedberg, PhD, professor of environmental health sciences in the School of Public Health at the University of Minnesota, told CIDRAP News. “It would be useful to have more open communication and more rapid assessment of what’s going on.” 

The built-in delay associated with Cyclospora lengthens the investigation, slowing news about an outbreak. Still, there’s been only a sluggish trickle of information from the FDA and the Centers for Disease Control and Prevention (CDC). While it’s believed cases from the large Cyclospora outbreak were first reported on May 1, the CDC didn’t issue a Health Alert Network advisory about it until July 14, about 10 weeks later.  

“The lack of federal public comment has been very challenging, because people have looked to the federal government to give them clarity of what’s happening,” Osterholm said. “That absence has allowed this big black hole for information.” 

As former director for the of the CDC’s Influenza Division and later, the National Center for Emerging and Zoonotic Infectious Diseases, Daniel Jernigan, MD, MPH, understands the importance of regular communication during outbreaks to keep the public updated and assuage fears. 

“Anytime you have a void of information, it gets filled with rumor,” Jernigan said. “If you’re not out there regularly communicating, then it does open a gap.” 

It can be tough for public health officials to balance how much to share, especially when there are still so many unknowns. 

“In a period of uncertainty, public health officials and regulatory officials really don’t want to overstate what they know,” Hedberg said. “But it doesn’t help when there’s a lot of information floating around the edges, and the main officials responsible for tracking it aren’t really commenting on it.” 

Jernigan agrees. “It’s OK for them to be careful,” he said. “That doesn’t mean you have to be quiet.” 

Why Cyclospora is hitting hard this year 

As of today, Michigan, the hardest-hit state, is reporting 9,680 cases of cyclosporiasis, which is what infection with Cyclospora is called. The total includes 160 hospitalizations, according to the state’s Department of Health and Human Services. Northwestern Ohio is reporting 2,785 cases, with 1,173 cases in Lucas County, says the Toledo Lucas County Health Department. 

These numbers far surpass national cases in years past. Nationwide, there were 4,500 cases in 2023 and 3,500 in 2024, the FDA said last week. 

It’s unclear why the number of cyclosporiasis cases this year is so high.  

“The short answer is we don’t know why,” Hedberg said. “I think there’s several things that are contributing to that.” 

There are some possible reasons more people are being diagnosed as having cyclosporiasis. Culture-independent diagnostic tests (CIDTs) to identify foodborne illnesses “make testing more available and faster and easier,” he explained. 

“The use of CIDTs has expanded greatly over the past decade,” Hedberg said. “We have the ability to identify cases in ways that weren’t readily available not that long ago.” 

As awareness of an outbreak spreads, people are more likely to visit their doctor if they have any symptoms of cyclosporiasis, which include bloating, stomach cramps, watery diarrhea, and nausea. 

“They see their illness as part of the outbreak,” Hedberg said. “They seek care, and then that further increases the amount of testing that gets done.” 

The source of the large outbreak, iceberg lettuce, likely contributes to higher numbers of cases, because it’s widely eaten.   

“If lettuce is contaminated and you have high volumes of consumption, then you’re going to have probably more exposures than we might have had with other less readily available [produce],” Hedberg said. 

When will the outbreak end? 

Taylor Farms recalled its iceberg lettuce on July 17, and the affected lettuce should no longer be available. Also, the way lettuce is grown likely means that new lettuce is coming from a different area of the farm, what’s often called a block. 

“When you’re dealing with produce, you’re harvesting every day, 365 days a year, and therefore you actually have to position those fields to be harvested at a given time,” Osterholm said. He is a consultant for Fresh Express, a supplier of bagged lettuce and salad kits. “You could have contamination on just several blocks based on contaminated irrigation water, for example, and it wouldn’t even affect a full ranch, let alone an entire region.” 

It’s possible that the nine-state outbreak is winding down.   

“In all likelihood, the first phase of the outbreak associated with lettuce from Mexico may well be in the waning phase,” Hedberg said. 

The epidemic curve, which the CDC shared on July 24, provides insight into the outbreak’s path. 

“There are two distinct peaks,” Hedberg said. “We’ve been sort of on the backside of the second peak.” 

The data delay could mean the outbreak is ongoing, “but if you look at the two outbreak peaks that are present, it would certainly be consistent with the main transmission event… having worked its way through the system,” he added. 

Still, there’s an ongoing trace-back investigation involved in the newly identified outbreak. “We’ll have to wait and see what that means,” Hedberg said.