The Highlights

• Cyclospora cayetanensis is spread by indirect fecal-oral route and occurs when people consume food or water that has been contaminated with infected human feces.
• Outbreaks have been frequently tied to consumption of raw, fresh produce, including herbs (basil), fruits (berries), bagged lettuce and snowpeas.
• C. cayetanensis stains poorly with both wet-mount and trichrome (permanent) stains used commonly in routine Ova & Parasite (O&P) examinations.
• Clinical microbiology labs should inform clinicians that the routine “O&P” will not readily detect Cyclospora and add a note to routine O&P result that this test will not readily detect Cyclospora, Cryptosporidium or Cystoisospora.
• Modified acid-fast or modified safranin stains of concentrated fecal smears can detect these poorly staining organisms; however, UV microscopy is significantly more reliable for detection of the oocysts.
• UV microscopy of concentrated stool wet-mounts is recommended for routine identification of Cyclospora in clinical specimens and should be performed when possible.
• Both lab-developed and FDA-approved molecular panels (PCR) that detect Cyclospora are available; some, but not all, GI panels include Cyclospora. Confirm that a GI panel specifically detects Cyclospora before testing.
• Report any detected/suspected organisms to your public health laboratory/department.

The Organism

Cyclospora cayetanensis is a protozoan parasite that infects the small intestine and can cause frequent, watery and sometimes explosive diarrhea. The infection is normally self-limiting, and humans are the only known hosts.

C. cayetanensis oocysts are spherical in shape and 8-10 mm in diameter (larger than Cryptosporidium, which is 4-6 mm). Infection is acquired when a person ingests food or water that has been contaminated with sporulated oocysts.

While some infections can remain asymptomatic, cyclosporiasis usually manifests as sudden, watery and often explosive diarrhea; cramps, nausea, loss of appetite and weight loss; body aches; fatigue and low-grade fever. Symptoms generally appear within a week of exposure, but incubation can range from 2 days to 2 weeks. Symptoms may also wax and wane in a repeating cycle that can last for weeks or months, if left untreated. This is a result of the parasite's unique life cycle. For details of this life cycle, see the CDC website.

C. cayetanensis is endemic in tropical and subtropical regions around the world. In the U.S., C. cayetanensis infections are not common; however, foodborne outbreaks of cyclosporiasis have been linked to various types of imported fresh produce, including bagged salad, fruits, specifically berries, herbs and vegetables like basil, cilantro, parsley, snowpeas, sugar snap peas and green onions.

The Current Outbreak

A multistate Cyclospora outbreak caught the attention of public health officials in May 2026 and is ongoing. A CDC Health Alert published on July 14, 2026, recognized 1,645 confirmed domestic cases of cyclosporiasis since May 1, 2026, and 5,100 additional suspected cases that require further testing to confirm. Prior to 2026, the highest number of annual cases on U.S. record was 4,700 in 2019. As case numbers continue to rise, accurate detection and reporting for this pathogen are supremely important.

Cyclospora Testing Microscopic Detection

Stool should be collected and fixed immediately (10% formalin or other appropriate single vial fixative). Specimens must be concentrated before examination. At least 3 specimens (each collected > 24 hours apart) should be examined for achieving the highest sensitivity.

Cyclospora is not usually detected by a conventional O&P examination (i.e., concentrated wet-mount & trichrome stain) but can be detected using a modified acid-fast (MAF) or modified safranin (MS) stains. Oocysts can also be detected using light microscopy of wet-mounts using differential interference contrast (DIC) microscopy (to provide structural details) or using UV fluorescent microscopy.

Using MAF, oocysts are round, measure 8-10 mm, stain pink (Figure 1A) or as ‘ghost cells’ (no stain, Figure 1B), and may be slightly wrinkled or collapsed on 1 or more sides. With MS, oocysts stain more consistently and are red/orange (Figure 1C). The MS stain requires boiling the safranin during staining and may be cumbersome for many laboratories. Detailed staining procedures for both of these stains can be found on CDC's website.

With wet-mount/UV microscopy, oocysts appear as round, refractile structures with well-defined walls (Figure 1D). UV microscopy is more reliable than MAF due to the fact that all oocysts will naturally fluoresce, which mitigates the loss of sensitivity that can occur with a high abundance of “ghost cells” on MAF. Wet-mounts for UV microscopy should be prepared from the concentrated sample (without iodine). Blue fluorescence is seen from oocysts with UV light (330-365 nm filter), and green fluorescence can be seen with blue excitation (450-490 nm filter).

Key Points for UV Identification of Cyclospora:

1. Oocyst size and shape are very consistent (range only between 8-10 µM; round or slightly flattened on 1 side).
2. Oocyst color is very consistent (blue at 330-365 nm or green at 450-490 nm filters).
3. Do not prepare wet-mounts with iodine for UV microscopy. Oocyst autofluorescence is impaired in the presence of iodine.
4. Potentially positive samples should be sent to a public health laboratory or reference laboratory for confirmation of Cyclospora.

Molecular Detection

Molecular tests (e.g. PCR) are highly sensitive methods to detect Cyclospora in stool. Both lab-developed and FDA-approved panels that detect Cyclospora are available. However, most GI panels do not currently detect Cyclospora, so it is important that clinicians consult with their primary clinical laboratory to determine which molecular test is utilized and whether C. cayetanensiscan be detected.

Overall Testing Recommendations

Routine O&P, MAF or MS stains, and/or molecular detection should be performed when clinically indicated. In addition to routine testing, increased utilization of the UV microscopy of stool wet-mounts is recommended:

1. Perform UV microscopy of concentrated stool wet-mounts with all test orders that include a MAF or MS stain.
2. If routine UV microscopy of wet-mounts is not feasible due to limited resources, laboratories should make every effort to include UV microscopy during known C. cayetanensis outbreaks.
3. When C. cayetanensis suspicion is noted in the order requisition, laboratorians should ensure that appropriate detection methods have been ordered and UV microscopy should be included in the stool work-up.

Clinical microbiology labs should inform clinicians that the routine “O&P” examination will not detect Cyclospora. If possible, they should also consider including a comment with routine O&P results that this test will not readily detect Cyclospora, Cryptosporidium or Cystoisospora species and offer additional testing for these organisms when clinically warranted.

Cyclosporiasis is a nationally notifiable disease. Laboratories must communicate all positive results to their health department to determine if any additional or specific action is required.

Figure 1: Cyclospora oocysts visualized by microscopy. (A) MAF stained oocyst (B) oocysts without stain retention (‘ghost cells’) using MAF, (C) oocyst stained with MS, and (D) wet-mount under UV (330-365 nm). Images A-C captured at 1000X magnification, image D captured at 400X magnification. 

Source: Panels A, B, and D courtesy of M.R. Couturier, ARUP Laboratories/University of Utah. Panel C courtesy of DPDx: Laboratory Identification of Parasites of Public Health Concern

Figure 2: A representative 2017 Cyclospora-positive stool sample. (A) Rare ‘ghost cell’ oocyst with a slightly wrinkled center detected on trichrome stain at 1,000X magnification. (B) Abundant oocysts of the corresponding wet preparation at 400X magnification. Red arrows indicate example oocysts (NOTE: not all oocysts have been indicated). 

Source: M.R. Couturier, ARUP Laboratories/University of Utah

Acknowledgements: Written by Marc Roger Couturier, Ph.D., D(ABMM), ARUP Laboratories/University of Utah, Salt Lake City, UT; Laura M. Filkins, Ph.D., ARUP Laboratories/University of Utah, and the ASM Public and Scientific Affairs Board Committee on Laboratory Practices. September, 2017. Updated by ASM Staff. July 2026.