The Centers for Disease Control and Prevention (CDC) has issued a nationwide Health Alert Network (HAN) advisory after an unusually large increase in domestically acquired cases of cyclosporiasis (Cyclospora infection). As of July 13, 2026, CDC had received reports of 1,645 laboratory-confirmed U.S. cases across 34 states and was aware of more than 5,100 additional reports that required further analysis to determine whether they met the definition of domestically acquired cyclosporiasis. This is substantially higher than the 249 domestically acquired cases reported during the same period in 2025. Public health officials are also investigating several outbreaks, including a multistate outbreak involving more than 400 reported cases in Michigan, Ohio, West Virginia, and Kentucky.
Cyclosporiasis is a gastrointestinal illness caused by the microscopic parasite Cyclospora cayetanensis. People become infected by consuming contaminated food or water, most commonly fresh produce. Symptoms typically begin about one week after exposure and include prolonged watery diarrhea, abdominal cramping, nausea, fatigue, loss of appetite, and weight loss. Without treatment, illness may last for weeks or longer and can follow a relapsing course. Because routine stool ova and parasite examinations may not reliably detect Cyclospora, the CDC is urging clinicians to specifically request diagnostic testing when the infection is suspected.
Although cyclosporiasis is usually not life-threatening, it can cause more severe or prolonged illness in people who are immunocompromised.
The CDC advises that individuals with immunocompromising conditions may require longer treatment courses than immunocompetent patients, while published reviews identify infants, older adults, and immunocompromised individuals among those at highest risk for severe disease.
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For people living with autoimmune diseases, particularly those taking biologics, corticosteroids, or other immunosuppressive medications, the CDC alert also serves as an important reminder that persistent diarrhea is not always caused by autoimmune disease activity. While cyclosporiasis can affect anyone, in people with Crohn’s disease or ulcerative colitis, it can closely resemble an inflammatory bowel disease (IBD) flare, potentially delaying diagnosis or leading to unnecessary escalation of immunosuppressive treatment if an infectious cause is not considered.
A recent 2025 case report illustrates this challenge. A woman with ulcerative colitis continued to experience worsening diarrhea despite biologic therapy, and her symptoms were initially presumed to represent an IBD flare. Stool testing ultimately identified Cyclospora cayetanensis, and after receiving targeted antiparasitic treatment, her symptoms improved rapidly, allowing her biologic therapy to be safely resumed. The authors concluded that clinicians should maintain a broad differential diagnosis for persistent diarrhea in immunosuppressed patients, even in regions where cyclosporiasis is uncommon.
Understanding when symptoms may reflect an infection rather than autoimmune disease activity, recognizing when additional testing may be needed, and taking steps to reduce infection risk can help prevent complications and delays in appropriate treatment.
Citations
Centers for Disease Control and Prevention. Increase in Reported U.S. Cyclospora Infections — Health Alert Network (HAN) No. 00531. July 15, 2026. Accessed July 16, 2026. https://www.cdc.gov/han/php/notices/han00531.html
Connor, B. A., Johnson, E. J., & Soave, R. (2001). Reiter syndrome following protracted symptoms of Cyclospora infection. Emerging infectious diseases, 7(3), 453–454. https://doi.org/10.3201/eid0703.010317
Banasik, E., Dobrowolska, A., Woźnicka-Leśkiewicz, L., & Eder, P. (2025). Diagnostic Challenges of Cyclosporiasis in Chronic Diarrhea: A Case Study. Microorganisms, 13(9), 2209. https://doi.org/10.3390/microorganisms13092209
Li, J., Wang, R., Chen, Y., Xiao, L., & Zhang, L. (2020). Cyclospora cayetanensis infection in humans: biological characteristics, clinical features, epidemiology, detection method and treatment. Parasitology, 147(2), 160–170. https://doi.org/10.1017/S0031182019001471
