What to know about cyclosporiasis: the foodborne parasite | Outbreaks

Cyclosporiasis is an intestinal infection caused by Cyclospora cayetanensis. This is a single-celled parasite in a group called coccidia [18].

The illness is classified as a foodborne parasitic infection. It is sometimes confused with other intestinal parasites like Giardia or Cryptosporidium, but Cyclospora is a distinct organism with its own life cycle and transmission pattern [18].

Cases occur worldwide but are more frequently reported in tropical and subtropical regions [16]. In the United States, most cases are linked to imported fresh produce [19].

Cyclosporiasis spreads through food or water contaminated with mature oocysts, the parasite’s dormant, shell-like form that spreads through feces [18].

Freshly passed oocysts are not infectious. They need about 1-2 weeks to mature in soil, water, or on produce, before they can infect the next person [17]. Because of this delay, cyclosporiasis rarely spreads directly from person to person (unlike salmonella or norovirus) [17].

In the US, outbreaks are almost always linked to fresh produce imported from, or grown in, regions where irrigation water or field handling may have been contaminated by human waste [18], [19].

This has historically included raspberries, basil, cilantro, snow peas, and mesclun lettuce mixes [5], [19]. In the 2026 outbreak, iceberg lettuce was also a source of infection [13], [14].

Cyclospora cayetanensis was first documented in 1979 by R.W. Ashford, a researcher who examined stool samples from three people in Papua New Guinea.

He described an unfamiliar parasite from a family called coccidia, single-celled organisms known for infecting the gut. He noted it might be related to two other parasites in that family, Toxoplasma or Hammondia [1].

Through the 1980s, researchers called it a “cyanobacterium-like body,” or CLB. Cyanobacteria are better known as blue-green algae. Under a microscope, that’s what the parasite looked like at this early stage. Scientists could only see its dormant, unhatched form back then. This is a small shelled structure called an oocyst [4].

In 1992, Ynes Ortega and colleagues coaxed the organism through its full life cycle in the lab for the first time. They triggered the oocyst to mature (a process called sporulation) and triggered it to hatch (called excystation).

Observing this complete cycle allowed them to classify the parasite correctly. They proposed the name Cyclospora cayetanensis in 1993, honoring Universidad Peruana Cayetano Heredia in Lima, where much of the early research took place [2]. A complete description of its structure followed in 1994, which validated the name [3].

Cyclospora was known mainly as a cause of travelers’ diarrhea until 1996. That year, an outbreak in the US and Canada caused 1,465 cases across 20 US states, Washington DC, and two Canadian provinces [6]. Investigators traced it to raspberries imported from Guatemala [6]. This outbreak established cyclosporiasis as a domestic foodborne threat in North America, not just a risk tied to travel abroad [5].

Recurring raspberry-linked outbreaks through the rest of the 1990s led the CDC to make cyclosporiasis a nationally notifiable disease starting in January 1999 [17].

Cyclospora is endemic in parts of Latin America (Guatemala, Haiti, Peru, Brazil, Mexico, Venezuela), Egypt, sub-Saharan Africa, the Indian subcontinent (notably Nepal), and parts of Southeast Asia, including Indonesia [16], [19].

In traditionally non-endemic countries, like the US, most historical cases were travel-associated. They were often related to trips to Mexico, the Dominican Republic, Guatemala, Haiti, Peru, or Nepal [16].

Since 1996, domestically acquired foodborne outbreaks tied to imported produce have been the dominant pattern [5], [19].

2026 is the largest cyclosporiasis outbreak year the US has recorded [13], [15].

Notable outbreaks

1996, US/Canada: 1,465 cases across 20 states, DC, and 2 Canadian provinces, tied to Guatemalan raspberries. This outbreak established cyclosporiasis as a foodborne threat in North America [6].

2000, Philadelphia: The first outbreak where Cyclospora DNA was recovered directly from the implicated raspberries, in addition to epidemiological evidence [9].

2013, US: 643 cases across 25 states, from two concurrent outbreaks: bagged salad mix from Taylor Farms de Mexico (Iowa and Nebraska, via Olive Garden and Red Lobster) and fresh cilantro from Puebla, Mexico (Texas) [10].

2018, US: A McDonald’s salads outbreak (511 cases, 15 states) alongside a separate Del Monte vegetable tray outbreak (roughly 237 to 250 cases, 4 states) [11], [12].

2026, US: The largest on record, with 18,000+ suspected cases across 45 states. This includes a 1,947-case cluster across 9 states tied to Taco Bell and Taylor Farms iceberg lettuce [13], [14], [15]. In August 2026, Michigan health officials reported two deaths connected to the outbreak, the first cyclosporiasis deaths confirmed in the US [22], [23].

GIDEON offers human-verified data on cyclosporiasis outbreaks, cross-country notes, clinical notes with citations, and much more.

Infection starts when a person swallows an oocyst (the tiny, tough capsule that protects the parasite) [18].

Once the oocyst reaches the small intestine, it breaks open. The parasite escapes and burrows into the cells lining the gut wall where it begins to multiply [20].

This process damages the gut lining, leading to inflammation. It flattens villi in the intestine, the small finger-like structures that help our bodies absorb nutrients [19], [20].

This damage to the small intestine helps explain the main symptoms of cyclosporiasis. Watery diarrhea, bloating, and malabsorption happen because the gut wall does not work well when infected. This inflammation can also result in weeks of lingering fatigue [20].

During this time, new oocysts form in the intestine. They exit from the body in feces, but are not infectious yet. They need 1-2 weeks in the environment to mature before they infect someone else.

This delay is why the illness rarely spreads directly from person to person [17], [18].

Symptoms typically begin about a week after exposure, though the timing can range from 2 to 14 days [16].

Cyclosporiasis symptoms include [16], [17]:

• Watery diarrhea or explosive diarrhea (one of the most common symptoms)
• Abdominal cramping and bloating
• Nausea and loss of appetite
• Weight loss
• Vomiting
• Low-grade fever
• Prolonged fatigue

One unusual feature sets cyclosporiasis apart from most foodborne illnesses. When left untreated, symptoms tend to improve but return. This cycle can stretch for a month or more [17]. Feeling better for a day or two does not necessarily mean the infection is gone.

It’s important to note that not everyone who gets infected gets sick. In particular, people who live in areas where the parasite is common all year round can build partial protection against symptoms [18], [19].

Death from cyclosporiasis is rare, and for most of the illness’s documented history in the US, no fatalities had been confirmed [16] until August 2026.

Typically, when severe outcomes do occur, they tend to trace back to dehydration from prolonged, heavy diarrhea rather than the parasite itself. They also disproportionately affect people who are older or already living with a chronic illness [22], [23]. Because of this, fluid intake, and prompt medical attention is an important part of managing the infection, particularly in vulnerable groups.

Standard stool tests do not automatically check for Cyclospora. A lab typically needs a specific request, or testing methods sensitive enough to catch it, since it is easy to miss on a routine exam [16].

Labs can detect the parasite a few different ways [20]:

• Special staining techniques that make the oocysts visible under a microscope, sometimes turning them bright pink-red
• A method that uses ultraviolet light, since oocysts glow under UV, considered one of the more reliable microscopic approaches [21]
• Molecular testing, which detects the parasite’s genetic material directly and tends to catch infections that microscopy misses, especially when few parasites are present [18], [20]

Because the parasite is not shed constantly, one stool sample is often not enough. Testing at least three samples, collected more than a day apart, gives a more reliable result. A single negative test does not rule out infection [16].

The standard treatment is a combination antibiotic called trimethoprim-sulfamethoxazole. The typical course lasts 7 to 10 days, though a healthcare provider determines the exact dose and duration for each person [16].

People with HIV or other conditions that weaken the immune system may need a longer course, since their bodies can take more time to clear the parasite [16].

Note

Not everyone can take this medication. Those with a sulfa allergy (an allergy to a group of drugs that includes this treatment) may be prescribed ciprofloxacin instead. Another option, nitazoxanide, may come up when sulfa allergy and ciprofloxacin resistance overlap [20].

People without symptoms generally do not need treatment. However, those who work in food handling may need medical clearance before returning to work, depending on local health guidelines.

Left untreated, the infection often clears on its own eventually, but this could take weeks. Symptoms may also resurface again [17].

There is no vaccine for cyclosporiasis [20].

Wash vegetables and fruit but be aware that washing does not reliably remove Cyclospora. Its dormant form is sticky and lodges in microscopic crevices on leafy greens and berries, resisting standard rinsing and even chlorine washes [18].

Cooking works better. Heating food to at least 158°F (70°C) kills the parasite [14]. However, this is not usually an option for foods eaten raw, like lettuce, berries, and herbs. This is part of why these foods keep showing up in outbreaks [19].

Since washing and cooking both fall short for raw produce, prevention efforts focus further upstream, on farms and supply chains: worker hygiene, safe irrigation water, sanitation, and traceability systems that can track contamination back to its source [18], [19].

Since cyclospora is spread through feces, it is also important to wash hands well with soap before touching food.

During an active outbreak, a few steps can lower risk [14]:

• Check recall notices and avoid any implicated product or lot
• Treat “prewashed” or “triple-washed” labeling with caution, since neither guarantees protection
• Consider whole heads of lettuce over bagged salad, since contamination in a bagged product can spread across a larger batch
• Apply standard food and water precautions when traveling to regions where the parasite circulates year-round

Please consult a healthcare provider if you experience symptoms of cyclosporiasis.

Cyclospora has been around for decades and rarely spreads from person to person. However, in 2026, it caused the largest cyclosporiasis outbreak the US has ever recorded, including two deaths [13], [15], [22], [23].

Part of what makes this parasite tricky is that it does not behave like the stomach bugs most people know. Washing produce won’t reliably remove it, and a standard lab panel test may miss it.

A large part of preventing its spread depends on public health responses. Identifying the source of clusters of outbreaks in the industrial food chain is critical for outbreak containment. Preventive measures should include training for people who work in food handling to wash their hands thoroughly after using the restroom (since the parasite travels through feces).

Q: Is cyclosporiasis contagious from person to person?

Rarely. The parasite is shed in feces in a dormant form that needs 1-2 weeks before it can infect someone else. This delay makes it less likely to spread from person to person [17].

Q: Can I get cyclosporiasis even if I wash my produce well?

Yes. Washing removes general dirt and debris, but it does not reliably remove Cyclospora. Even chlorine does not kill it [18]. However, it is important to wash your produce and your hands with soap before handling food.

Q: How long does cyclosporiasis last if it is not treated?

It can last from a few days to a month or more. Symptoms may improve, and then return, in a relapsing pattern [17].

Q: What foods have been linked to cyclosporiasis outbreaks?

Historically, raspberries, basil, cilantro, snow peas, and mesclun lettuce mixes [5], [19]. In the 2026 outbreak, one source was iceberg lettuce from central Mexico [14].

Q: Will a regular stool test catch cyclosporiasis?

Not always. Specific tests are required and often, several stool samples may be collected over a few days to confirm the presence of the parasite. This is because the parasite is not shed constantly [16].

Q: What is the treatment for cyclosporiasis?

Antibiotics like trimethoprim-sulfamethoxazole (sold as Bactrim or Septra) is the first-line treatment. Ciprofloxacin or nitazoxanide may be alternatives for people with a sulfa allergy [16], [20]. Please consult a healthcare provider to get tested and receive treatment.

Q: Who is most at risk?

Anyone eating contaminated produce, plus travelers to parts of Latin America, Africa, and South or Southeast Asia where the parasite is common [16]. Risk does not skew strongly by age, though people with weakened immune systems may get sicker or stay sick longer [17].

Q: Is there a vaccine for cyclosporiasis?

There is no vaccine for cyclosporiasis [20].

Q: Why was 2026 such a significant year for cyclosporiasis in the US?

The 2026 US outbreak became the largest outbreak on record, with more than 18,000 suspected cases by late July 2026. One cluster of nearly 2,000 cases was tied to Taco Bell and Taylor Farms iceberg lettuce [13], [14], [15]. 2 deaths were reported in August 2026.

Q: Can cooking kill Cyclospora?

Yes, heating food to at least 158°F (70°C) destroys the parasite. This is not an option for foods normally eaten raw, like lettuce and berries [14].

Q: Can cyclosporiasis be fatal?

Health authorities have long described the illness as not typically life-threatening [16]. However, the first two cyclosporiasis deaths in the US were reported in Michigan in August 2026. The deaths were related to people who had underlying health conditions, which may have contributed to severe dehydration from the infection [22], [23]. As with most foodborne illnesses, older adults and those who are immunocompromised or have chronic health conditions are at a higher risk of a more severe infection.

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