The U.S. is experiencing a significant surge in cyclosporiasis cases, with 1,645 confirmed infections reported across 34 states since May 2026, compared to just 249 cases by the same time last year. This parasitic gastrointestinal illness, spread through contaminated food and water, has hospitalized 141 patients (9% of those with available data), though no deaths have been reported. The Centers for Disease Control and Prevention (CDC), Food and Drug Administration (FDA), and state health departments are actively investigating multiple clusters to identify common sources.

What Is Cyclosporiasis and How Do People Get Infected?

Cyclosporiasis is caused by a microscopic parasite called Cyclospora that contaminates food or water. Unlike many foodborne illnesses, cyclosporiasis is not typically spread directly from person to person. Previous outbreaks have been linked to consuming contaminated fresh produce, and the CDC considers May 1 through August 31 the annual cyclosporiasis season when case counts naturally rise.

The infection develops gradually. Symptoms typically begin about one week after exposure, though they can appear anywhere from two to fourteen days after contact with the parasite. Without treatment, the illness can follow a pattern of improvement and relapse that lasts from a few days to a month or longer.

What Symptoms Should Prompt a Doctor's Visit?

Recognizing cyclosporiasis symptoms is critical because the illness is often underdiagnosed and underreported, meaning the true number of cases is likely higher than reported figures. The most common symptom is watery diarrhea, which can be frequent and persistent. Other frequent symptoms include loss of appetite, weight loss, bloating, nausea, and fatigue. Less common symptoms include low-grade fever and vomiting. In severe cases, complications can develop, including malabsorption (difficulty absorbing nutrients), cholecystitis (inflammation of the gallbladder), and reactive arthritis (joint inflammation following infection).

The CDC emphasizes that clinicians should consider cyclosporiasis in patients presenting with prolonged or relapsing watery diarrhea, particularly during the May through August season, even if they have no history of international travel. This is especially important because many cases in the current outbreak are domestically acquired, meaning people became infected within the United States.

How to Protect Yourself and Get Proper Diagnosis

• Seek medical attention promptly: Visit a clinician if you experience prolonged or watery diarrhea, especially if it lasts more than a few days, to rule out cyclosporiasis or other serious conditions.
• Request specific testing: Laboratory detection of Cyclospora in stool samples can be challenging, and standard ova and parasite exams might not reliably detect the parasite. Ask your doctor to specifically request Cyclospora testing, including molecular (PCR-based) diagnostic testing where available, which improves detection accuracy.
• Wash fresh produce thoroughly: Reduce your risk by washing fresh produce under clean running water before consumption, as previous outbreaks have been linked to contaminated fresh fruits and vegetables.
• Stay hydrated: If you develop diarrhea, drink plenty of fluids to prevent dehydration, especially if diarrhea is frequent or severe.

The CDC notes that laboratory detection challenges mean cyclosporiasis is likely underdiagnosed. Clinicians should specifically request diagnostic testing for Cyclospora when it is clinically suspected, rather than relying solely on routine examinations.

What Treatment Options Are Available?

Once cyclosporiasis is confirmed through proper testing, treatment is straightforward and effective. The standard treatment is trimethoprim-sulfamethoxazole (TMP-SMX), an antibiotic combination, taken for seven to ten days for immunocompetent adults and children over two months of age. Patients with immunocompromising conditions may require longer treatment courses. Clinicians should consult current CDC clinical guidance for recommended dosing based on individual patient factors.

The current outbreak has affected people across a wide age range. Case-patients have ranged from two to ninety-five years old, with a median age of forty-four years, and fifty-six percent were female. The CDC is working closely with the FDA and state health authorities to investigate multiple clusters of cyclosporiasis, including one outbreak with more than four hundred cases in at least four U.S. states that appear to be epidemiologically linked, suggesting a possible common source of infections.

Because cyclosporiasis is often underdiagnosed and underreported, the true number of illnesses is likely substantially higher than the 1,645 confirmed cases reported to the CDC. The agency is aware of more than 5,100 additional cases that require further analysis to confirm whether they represent domestically acquired cyclosporiasis.

If you experience symptoms consistent with cyclosporiasis, especially during the May through August season, contact your healthcare provider and mention the possibility of this parasitic infection. Early diagnosis and appropriate treatment with TMP-SMX can resolve the illness and prevent complications.