What You Need to Know About Cyclosporiasis
In July 2026 a large multistate outbreak in the United States thrust an obscure intestinal illness known as cyclosporiasis into the national spotlight. The first cases were reported in May, and by early July health officials in more than 30 states were investigating cases linked to the causative parasite, Cyclospora cayetanensis. Some 19,883 cases were confirmed by September 11, according to the U.S. Centers for Disease Control and Prevention (CDC). That same day, the outbreak was declared over.
Case counts were likely higher during the 2026 outbreak, based on reporting by individual states. Cyclosporiasis is difficult to track, however, owing especially to challenges in detecting the parasite and optional state-level surveillance. Moreover, as an illness, cyclosporiasis can be surprisingly difficult to recognize. Many infected people assume they have a routine stomach illness and never seek medical attention. Here is what you need to know about cyclosporiasis.
What is cyclosporiasis?
Cyclosporiasis is an intestinal illness caused by the microscopic parasite C. cayetanensis. The small intestine is targeted by this parasite. Upon infection, the normal processes facilitating the absorption of nutrients and water are disrupted, often leading to prolonged digestive illness. Cyclosporiasis occurs worldwide, though cases generally are concentrated in tropical and subtropical regions. It also has become increasingly recognized as a cause of waterborne and foodborne illness. Cyclosporiasis is rarely spread directly from between individuals, sinceC. cayetanensis matures outside the human body before it is able to infect another person.
" height="20" alt="HEW Logo">
What causes cyclosporiasis?
Cyclosporiasis develops following the consumption of food or water that contains oocysts of Cyclospora. Oocysts are tough and thus represent the environmentally resistant stage of the Cyclospora life cycle. Types of foods likely to be contaminated with the parasite include fresh fruits, leafy greens, herbs, and other produce; these foods are most often linked to outbreaks when they are eaten raw and particularly when they have been irrigated or washed with contaminated water. The 2026 outbreak appeared to be linked specifically to contaminated iceberg lettuce.
Once inside the digestive tract, the parasite finds its way into the lining of the small intestine. There, it multiplies, resulting in a new generation of oocysts. These new oocytes are shed in the feces. They are not immediately infectious, however. Their infectious nature develops only after they have undergone a necessary maturation phase in the environment. This characteristic distinguishes Cyclospora from many other foodborne pathogens.
What are the symptoms of cyclosporiasis?
Symptoms typically appear about one week following infection, although the timing can vary. Frequent, watery diarrhea is the primary symptom, sometimes lasting for multiple weeks or even recurring in the absence of treatment. There are various other common symptoms, ranging from abdominal cramping, bloating, and nausea to fatigue and low-grade fever. Some individuals experience vomiting and muscle aches, whereas others—especially those who are healthy—may have few or no symptoms. Cyclosporiasis can be problematic for individuals with weakened immune systems, where illness can be more severe and prolonged.
How is cyclosporiasis treated?
Cyclosporiasis is treated primarily with the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX), which is highly effective against Cyclospora infection. Prolonged diarrhea requires supportive care, typically in the form of fluids and electrolytes, which help prevent dehydration. Infection usually subsides over time when the immune system is functioning properly. Even with treatment, however, relapse can occur. In severe cases, symptoms can continue for a month or longer.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
