As of August 10, the ongoing Cyclospora outbreak in the United States has resulted in 13,895 laboratory-confirmed domestic cases, according to the CDC, with at least 10,455 additional reported cases still awaiting confirmation or further investigation. The CDC is investigating multiple clusters of cyclosporiasis cases, including a multistate outbreak affecting nine states linked to iceberg lettuce sourced from central Mexico.
As the outbreak continues to evolve, clinical laboratories remain essential to detecting infections, supporting outbreak investigations, and protecting public health.
What is Cyclospora and how does it spread? Understanding cyclosporiasis, symptoms, and transmission
Cyclospora cayetanensis is a coccidian protozoan parasite that infects the epithelial cells lining the small intestine, causing cyclosporiasis. It is the only Cyclospora species known to infect humans. Infection occurs when people ingest food or water contaminated with infectious oocysts.
Unlike many other infections, cyclosporiasis is not typically spread directly from person to person. The parasite matures outside the host before becoming infectious.
Symptoms can include appetite loss, low-grade fever, fatigue, nausea, watery diarrhea, abdominal cramps, vomiting, and, in severe cases, bloody stool and high fever.
Because the transmission occurs via the fecal-oral route, standard hygiene and food safety practices can help prevent cyclosporiasis risk. The CDC emphasizes staying informed about food safety alerts and avoiding recalled foods to reduce your risk of Cyclospora infection.
What we know about the 2026 Cyclospora outbreak
Cyclosporiasis outbreaks have occurred in the US for decades. Case numbers typically spike from late spring through summer when warm temperatures facilitate maturation of the Cyclospora oocysts. Historically, cyclosporiasis outbreaks in the US have been frequently linked to contaminated fresh produce, including leafy greens, fresh herbs, berries, and other fruits and vegetables. What distinguishes the current outbreak is its size, multistate impact, and and the ongoing investigation into a potential common source.
The current outbreak prompted a public health investigation in May 2026, as cyclosporiasis cases began to surge across multiple states. As of July 28, the CDC has received reports of 6,707 laboratory-confirmed domestic cases of cyclosporiasis associated with a multistate outbreak affecting nine states—Illinois, Indiana, Kansas, Kentucky, Michigan, Ohio, Oklahoma, Pennsylvania, and West Virginia.
Epidemiological investigations have linked the outbreak to contaminated iceberg lettuce.
The agency is also aware of more than 11,500 additional reported cases that are not yet confirmed or require further investigation, including review to determine whether cases are associated with international travel. Many of these additional cases have been reported by Michigan and Ohio.
To date, no deaths associated with the outbreak have been reported.
Responding to the Cyclospora outbreak: diagnostic testing and challenges for clinical laboratories
Common diagnostic tests performed for Cyclospora detection:
Microscopy tests
Conventional microscopy-based diagnosis relies on detecting Cyclospora oocysts in clinical stool specimens.
- Stained Microscopy: acid-fast staining (colors oocysts pink/red) is most commonly used; modified safranin staining is another option (stains oocysts orange-red).
- Fluorescence microscopy: utilizes the natural fluorescence of oocysts. Unstained stool wet mounts fluoresce bright blue or green under UV light. Suspected oocysts are then confirmed using bright-field, phase-contrast, or differential interference contrast microscopy to verify their distinct morphology.
Microscopy remains useful for Cyclospora diagnosis but has several limitations:
- Specialized skills: Sample preparation and identification is a labor-intensive process requiring experienced lab personnel. Limited expertise and familiarity with organism morphology can lead to missed detections.
- False positives/artifacts: Although highly sensitive, UV fluorescence causes false positives. Unstained plant matter, fungal spores, and non-pathogenic coccidia can mimic Cyclospora oocysts, leading to misidentification.
- Variable staining: Inconsistent acid-fast or safranin staining causes unevenly colored oocysts, thus complicating microscopic interpretation.
Molecular tests
Molecular tests, including qPCR-based assays, provide clinical labs with sensitive and targeted detection of Cyclospora DNA in stool. These robust tests are available through commercial/reference/stand-alone laboratories or public health laboratories, as either lab-developed tests (LDTs) or FDA-approved commercial in vitro diagnostics (IVDs), including multiplex panels such as the BioFire FilmArray Gastrointestinal Panel and the QIAstat-Dx Gastrointestinal Panel 2.
Molecular testing overcomes microscopy limitations through several key advantages:
- Improved detection: Irregular oocyst shedding requires an expert microscopist and multiple-day sampling for Cyclospora detection. In contrast, PCR accurately detects the parasite from a single sample, simplifying and speeding up diagnosis.
- Faster results: PCR reduces disease burden by delivering actionable results within hours as compared to traditional microscopy methods that take up to several days.
- Broader detection: Multiplex PCR testing is valuable for Cyclospora because its clinical presentation overlaps with other microbial and parasitic gastrointestinal infections. By testing one stool sample for multiple pathogens simultaneously, labs can pinpoint the cause of illness, especially in outbreak settings.
- Supporting antimicrobial stewardship: Tying the above-mentioned advantages together, missed or delayed detections can lead to empiric treatment with broad-spectrum antibiotics that do not effectively target the parasite. With no vaccine currently available against Cyclospora, rapid diagnosis enables clinicians to make informed treatment decisions and ensure that patients receive targeted therapy with trimethoprim-sulfamethoxazole (TMP-SMX).
What diagnostic challenges remain despite advances in molecular testing for Cyclospora?
Molecular testing has revolutionized gastrointestinal infections testing. However, effectiveness of any diagnostic tool depends on time of testing, type of testing, and what’s included in the multiplex testing panel.
Missed testing window
Some people infected with Cyclospora remain asymptomatic, while others develop delayed symptoms approximately one week after infection. Because the incubation period can range from two days to two weeks or longer, patients may have difficulty connecting their illness to a specific food exposure, complicating outbreak surveillance and investigations.
Exclusion from routine testing
Cyclospora is not often included in routine parasite screens or commercially available multiplex PCR panels. Consequently, a negative result from a panel lacking C. cayetanensis cannot rule out cyclosporiasis diagnosis. Therefore, labs must explicitly select multiplex panels with this target to avoid false negatives, especially during outbreaks.
Looking ahead: a One Health approach to combating Cyclospora
The 2026 Cyclospora outbreak highlights the importance of a One Health approach that brings together expertise and collaboration across disciplines.
Clinical laboratories are vital in enabling early diagnosis and providing positivity and trend data that can help public health officials detect and investigate outbreaks. However, impactful progress calls for coordinated efforts and real-time data sharing across clinical medicine, public health, food safety, environmental science, agriculture, research, and industry.
As Samir Assar, PhD, director of the FDA’s Division of Produce Safety, noted during an “FDA Conversation on Cyclospora” discussing the agency’s Cyclospora Task Force, “It’s critical that we continue to work with our stakeholders to share data and research that will contribute much-needed information we can all benefit from.”
Echoing this collaborative approach, Alexandre da Silva, PhD, senior biomedical research/biomedical product assessment service expert, added, “We’ve been fortunate to have help from our state, local, industry, and federal partners who are all committed to finding solutions to this issue.”
Together, these partnerships and efforts can strengthen surveillance, improve outbreak response, and prevent future infections.
Note: This article was updated on August 10, 2026, to reflect the latest CDC surveillance data, including updated US case counts and information on the ongoing multistate Cyclospora outbreak linked to processed iceberg lettuce.
