Cyclosporiasis Cases Top 6,700: What Patients with Cancer Need to Know

Patients with cancer face a higher risk of severe illness from the outbreak of cyclosporiasis (a parasite tied to fresh produce) spreading across the United States, according to Dr. John Greene, with the Centers for Disease Control and Prevention (CDC) having confirmed 6,707 domestic cases across 45 states since May 1. More than 11,500 additional cases are still under investigation.

The parasite, Cyclospora cayetanensis, causes symptoms that can be indistinguishable from the side effects of certain cancer treatments. Examples include watery diarrhea, nausea, vomiting, cramping and bloating.

Can an individual catch cyclospora from someone in their household?

Unlike a respiratory virus, cyclospora does not spread from person to person.

"Because of the life cycle of cyclospora, person-to-person contact does not really occur," Greene, who is chair of the Infectious Diseases Program at Moffitt Cancer Center, said. "So, if there are millions of people infected, including your own household, you're not likely to catch cyclospora from them."

The parasite must be swallowed to cause infection, which makes contaminated food and water the only routes of transmission. Handwashing, produce washing, and awareness of what a patient eats matter far more than avoiding infected family members.

"Understanding this can help people find support from their family and friends instead of avoiding them because they're afraid they're going to catch it from somebody else," he said.

Which foods have been linked to the outbreak of cyclosporiasis?

The CDC has connected recent infections to imported fresh produce, including raspberries, snow peas, parsley, lettuce, basil, bagged salad, and cilantro. Much of it comes from Guatemala, Mexico and other regions where the parasite is common. Contamination can occur at any point along the way, during harvest, handling or transit, before it reaches a grocery store shelf.

Greene's advice centers less on how produce is washed and more on what patients buy in the first place.

"The bag of lettuce could come from a pile of 100 different heads of lettuce, as opposed to one lettuce head," he explained.

He recommends buying whole heads of lettuce rather than pre-bagged, pre-chopped greens, removing the outer leaves, and rinsing the rest thoroughly. Berries are harder to protect: It takes only 10 to 100 oocysts — the parasite's infectious form — to cause illness, and rinsing does not eliminate all of them.

Moffitt Cancer Center recommends refrigerating cut, peeled or cooked produce promptly, washing hands before food preparation, and cooking produce to an internal temperature of at least 158 degrees Fahrenheit.

"Rather than avoiding all vegetable products, which may not be healthy, you can be as safe as you possibly can by taking those steps," Greene said. He cautioned against bleach or excessive soap for washing produce, calling the practice unproven and potentially unsafe.

How can patients tell outbreak symptoms apart from cancer treatment side effects?

Symptoms typically appear within seven days of ingesting the parasite. The delay makes it difficult for patients to identify what caused their illness. Common signs include poor appetite, nausea, gas, fatigue, cramping, diarrhea, low-grade fever and weight loss, a list overlapping with side effects of cancer treatment.

Greene points to two clues that can help distinguish between symptoms from the outbreak and treatment-related side effects.

The first is timing. Patients who are well past a chemotherapy infusion, are between treatment cycles, or have no treatment-related explanation for new gastrointestinal symptoms; Greene suggests they get tested rather than wait it out.

The second is duration. Chemotherapy-related symptoms usually resolve within a day or two of an infusion. Symptoms lasting more than a week of warrant investigation.

"You're just going to have to look for more prolonged, unusual, severe symptoms, and weight loss is your key point to actually investigate a little more deeply, especially during an outbreak," Greene said.

Diagnosis requires a stool test, specifically a multiplex gastrointestinal panel, a PCR-based test screening for cyclospora alongside 19 other pathogens. A standard stool culture, Greene noted, detects bacteria but not parasites, and will miss the infection entirely.

What does treatment for cyclosporiasis involve?

Cyclosporiasis is treated with the antibiotic Bactrim (sulfamethoxazole and trimethoprim), typically for two to four weeks in patients with cancer, which is longer than the five- to 10-day course given to the general population.

"And if they're severely immune suppressed, we might include a longer duration of therapy," Greene said.

Patients who become dehydrated may receive intravenous fluids, along with antimotility drugs and anti-nausea medication. If symptoms don't respond to outpatient care, hospitalization may be necessary.

Why might symptoms linger after the cyclosporiasis infection clears?

Some patients continue to experience gastrointestinal symptoms long after the parasite is gone. Greene said the pattern is often mistaken for treatment failure.

The infection can disrupt the gut microbiome enough to trigger irritable bowel syndrome, he added, with symptoms lasting anywhere from several weeks to more than a year. The parasite itself is no longer present. The lingering symptoms come from the disruption left behind in the gut's normal flora and how that disruption affects the immune system.

A negative retest for cyclospora, or any other pathogen, is often the clearest evidence that the prolonged illness is not, in fact, ongoing infection. At that point, treatment shifts from targeting the parasite to managing the irritable bowel symptoms it left in its wake.

"So, making the correct diagnosis is key," Greene concluded.

References

1. CDC Health Alert Network (HAN): Domestically Acquired Cyclosporiasis Cases in Multiple U.S. States, 2026. Centers for Disease Control and Prevention., Posted: July 14, 2026.
2. Cyclosporiasis Outbreak with Unknown Source. Centers for Disease Control and Prevention. Posted: July 14, 2026.
3. Surveillance of Cyclosporiasis. Centers for Disease Control and Prevention. Posted: July 28, 2026.
4. News release. What To Know About the Cyclosporiasis Outbreak. Moffitt Cancer Center. Posted: July 20, 2026.

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