The CDC is warning of an increase in cyclosporiasis cases. Here’s what you need to know:
Cases of cyclosporiasis are increasing across the United States as authorities warn of contaminated produce and symptoms.
Mexico has denied responsibility for a nationwide outbreak of parasitic infections linked to lettuce that has sickened thousands of people in 41 U.S. states.
According to the Centers for Disease Control and Prevention, as of July 21, there were more than 4,000 laboratory-confirmed cases of cyclosporiasis, a disease that causes unpleasant symptoms such as explosive diarrhea, and the actual number of people infected is estimated to be more than 10,000. The U.S. Food and Drug Administration has linked the outbreak to lettuce grown by Taylor Farms in the central Mexican state of Guanajuato.
On July 21, the country’s Health Minister David Kaschenovich refuted the FDA’s claims. That same day, Health and Human Services Secretary Robert F. Kennedy Jr. said at a press conference that the outbreak was “under control.”
“So far, we have found no evidence that this is where it originated,” Kerschenovic told a news conference, according to Reuters. “But we are taking every precaution in case that happens.”
The Kennedy and Trump administrations have come under fire for cuts to relevant health agencies, with some critics pointing out that reduced surveillance and limited staffing have not only enabled the spread of Cyclospora, but also other recent outbreaks like the screwworm. Last year, the CDC scaled back a decades-old federal and state partnership monitoring foodborne illnesses, including those caused by Cyclospora.
Still, President Kennedy called the criticism “invalid.”
“We have cut back on the Food Net program, but it’s because of redundant oversight, and every state will say we’re still doing forensics,” he said during a July 21 briefing.
U.S. and Mexican authorities continue to search for the cause behind the outbreak, but the task is proving more troublesome than other recent foodborne illness outbreaks.
What exactly was a “false positive”?
Taylor Farms said in a July 19 statement that the FDA has “apologized” to the brand for a “false positive” test for Cyclospora on iceberg lettuce products from central Mexico. But food safety expert Bill Mahler said the company’s statements don’t tell the whole story and do little to prove liability in any way, which is not uncommon in investigations like this.
“A positive test doesn’t mean anything, a negative test doesn’t mean anything because the product they were testing is not the product that people are consuming,” Marler told USA TODAY. “Products that people have consumed, evidence that people have eaten…or things that have passed their best-before date and have been discarded.”
The FDA made a similar point in a July 20 post, saying, “To be clear, this false-positive test sample does not change the basis of FDA’s ongoing outbreak investigation or the overwhelming epidemiological data supporting Taylor Farms’ current voluntary recall.”
Even though food samples do not test positive for the pathogen, outbreaks are often traced back to the manufacturer, grower, or distributor. That happens, Marler said, not because they weren’t the root source, but because the culprit has already passed through the system or is hiding elsewhere, such as in the soil or water.
“Based on our 33 years of experience dealing with these cases, there are very few foods that can be tested during an outbreak,” he said. “Because by the time you know there’s an outbreak, the product is long gone. That’s especially true for fresh produce.”
So what does a false positive actually mean? It doesn’t matter much either way, Marler said, adding that Mexico’s claim of innocence is subject to similar uncertainty.
“A positive test does not necessarily mean with certainty that Taylor Farms is the source of the infection,” he said. “And a negative test does not exempt Taylor Farms from being the cause.”
So, is Taylor Farm safe?
No, it has not been conclusively proven that the Taylor farm was the source of the outbreak, but it has not been proven do not have To be.
As of July 20, the FDA still said tracking data shows shredded iceberg lettuce from a Taylor Farms location in central Mexico. Traceback data, information obtained through procedures such as interviewing sick people and used by researchers to track diseases through the food supply chain, is often the main tool used in Cyclospora outbreaks.
Taylor Farms de Mexico, Guanajuato, Mexico, announced in a voluntary recall that began July 17 that it would withdraw all iceberg lettuce from central Mexico from the U.S. market “out of an abundance of caution” as a measure “prompted” by the outbreak. “The company is actively removing the product involved. The company has stopped accepting product from the lot involved, has stopped distribution of iceberg lettuce from central Mexico, has notified customers, and continues to work with FDA, CDC, and state authorities,” the company said.
According to the CDC, Taylor Farms’ growing and processing facility in Mexico was the source of a major cyst disease outbreak in the United States in 2013 that sickened more than 600 people in 25 states and was traced to salad mix from Taylor Farms de Mexico in Guanajuato.
Marler explained that the technology used to identify the Taylor farm in this outbreak is the same as that currently in use.
Why health authorities are having a hard time identifying the culprit
The origins of cyclosporiasis are harder to trace than food poisoning for several reasons, primarily because, as USA TODAY previously reported, the same genetic tracing tools available for pathogens such as E. coli and Listeria monocytogenes cannot be used.
Today, most foodborne illness and infectious disease clusters are tracked by whole genome sequencing (WGS). WGS is a technique that examines and compares a pathogen’s unique genetic code to establish a unique “fingerprint.” This DNA “fingerprinting” allows scientists to determine whether the bacteria that make people sick are closely related, helping researchers link cases and trace outbreaks to a common source.
Because Cyclospora is difficult to culture, cannot be grown in the lab, and is generally found in small amounts in stool samples, the CDC is instead relying on a different sequencing system that targets selected genetic markers. This targeted genotyping can help determine which Cyclospora cases belong to the same outbreak, but unlike WGS, it typically cannot alone identify contaminated food or its origin.
In a media briefing on July 14, Dr. Gwen Biggerstaff, deputy director of CDC’s Division of Foodborne, Waterborne, and Environmental Diseases, called the method “useful for detection, but it is not as fast or accurate as whole-genome sequencing,” and acknowledged that it also cannot establish transmission routes with the same confidence as WGS. This is why sometimes no single grower, manufacturer, or seller can be identified, such as with the latest outbreak in 2024, which is linked to parsley.
How the FDA and CDC try to track and trace diarrhea bugs
In this and previous outbreaks, investigators relied heavily on what are called tracebacks, which essentially correspond to investigative efforts in food safety.
Once authorities identify groups of people who appear to be involved in the same outbreak, investigators trace back the food supply chain to find common sources. This is done first and foremost by interviewing the sick person about what they ate before becoming ill, but this is also complicated by the nature of the parasite. Because cysticercosis can have a long incubation period of two weeks or more, it can be difficult to remember what you ate during that time.
Once trends are identified, health agencies use a combination of patient interviews, genetic testing, and food supply chain records to “triangulate.” The answer lies in where these three types of evidence overlap.
“Investigating Cyclospora is particularly difficult and time-consuming,” Biggerstaff said, adding that the CDC and FDA are combining the pillars of surveillance and case counts, patient interviews and data tracking, laboratory testing and clinical alerts to determine the cause. “We want to be transparent that this is an active, ongoing investigation.”
