Cyclosporiasis laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Joseph Nasr, M.D.[2]; Alejandro Lemor, M.D. [3]
Overview
Cyclosporiasis is diagnosed by detecting Cyclospora cayetanensis oocysts or parasite DNA in stool specimens. Because oocyst shedding may be intermittent and low in quantity, a single negative specimen does not exclude infection. Three or more stool specimens collected on separate days, commonly at 2- to 3-day intervals over a period of more than 1 week, may be required when clinical suspicion remains high.[1][2]
Diagnostic methods include concentration of stool specimens followed by bright-field, phase-contrast, or differential interference contrast microscopy; ultraviolet fluorescence microscopy; modified acid-fast or modified safranin staining; and molecular testing using real-time polymerase chain reaction or multiplex gastrointestinal pathogen panels.[1][2]
Routine stool ova-and-parasite examinations and gastrointestinal molecular panels do not always include testing for Cyclospora. Clinicians should specifically request testing when cyclosporiasis is suspected and should confirm which organisms are included in the laboratory's testing platform.[3]
Laboratory Findings
- Stool examination remains a principal method for diagnosis.
- Oocyst shedding may be intermittent; therefore, a single negative stool specimen does not exclude cyclosporiasis.
- Three or more specimens collected at 2- to 3-day intervals over more than 1 week may be required in patients with persistent symptoms and high clinical suspicion.[1][2]
- Stool specimens should be concentrated before microscopic examination whenever possible to improve diagnostic sensitivity.[1][2]
- Recommended concentration methods include formalin–ethyl acetate sedimentation. Discontinuous sugar-gradient or Percoll-gradient centrifugation may also be used in specialized laboratories.[1]
- Routine ova-and-parasite testing may not automatically include specific examination for Cyclospora.
Stool Examination
Concentration of stool specimens
Because the number of oocysts in stool may be low, concentration of the specimen improves recovery. Modified acid-fast staining for intestinal coccidia should be performed on concentrated stool sediment when possible.[4][2]
Wet mount and light microscopy
On bright-field, phase-contrast, or differential interference contrast microscopy, Cyclospora oocysts are spherical and approximately 8–10 μm in diameter. They have a defined, relatively nonrefractile wall and may contain refractile internal globules or granular material.[5][1]
Cyclospora may be confused with Cryptosporidium, yeast, pollen, or staining artifacts. Size measurement is important because Cyclospora oocysts are usually 8–10 μm, whereas Cryptosporidium oocysts are generally approximately 4–6 μm.[1]
Shown below are images of Cyclospora oocysts in unstained wet mounts.
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Ultraviolet fluorescence microscopy
Cyclospora oocyst walls autofluoresce under ultraviolet illumination. With an excitation filter of approximately 330–365 nm, oocysts generally produce an intense blue fluorescence. With blue excitation at approximately 450–490 nm, a less intense green fluorescence may be observed.[1]
Ultraviolet fluorescence microscopy is a sensitive screening method and may be more sensitive than modified acid-fast staining. Its limitations include the need for a fluorescence microscope with appropriate filters and the absence of a permanent stained slide.[6]
Shown below are images of Cyclospora oocysts viewed under ultraviolet microscopy.
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Modified acid-fast stain
Modified acid-fast staining is widely used in clinical laboratories and provides a permanent slide that can be archived. However, staining is variable, which may reduce diagnostic sensitivity and lead to confusion with artifacts.[1]
- Oocysts measure approximately 8–10 μm.
- Oocysts may stain from light pink or red to deep purple.
- Some oocysts remain partially or completely unstained and may appear as pale or clear “ghost” forms.
- Oocysts may appear round, collapsed, or distorted and may contain granules or have a wrinkled wall.
- The blue-green or contrasting background counterstain helps distinguish oocysts from fecal debris.
Shown below are images of Cyclospora oocysts stained with a modified acid-fast stain.[7]
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Modified safranin stain
Modified safranin staining produces more uniform staining than modified acid-fast methods. Oocysts typically stain bright red to reddish-orange, which may reduce misidentification. Heating, traditionally performed with microwave assistance, is required for optimal staining.[8]
Shown below are images of Cyclospora oocysts stained with safranin.
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Trichrome stain
Routine trichrome staining is not reliable for detection or confirmation of Cyclospora oocysts. Oocysts may occasionally be noticed as clear, unstained, round, or wrinkled structures measuring approximately 8–10 μm, but suspected organisms require confirmation with ultraviolet fluorescence, a coccidian-specific stain, or molecular testing.[1][7]
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Molecular Testing
Molecular methods detect Cyclospora cayetanensis DNA in stool and may provide greater sensitivity than conventional microscopy, particularly when parasite burden is low.
- Real-time PCR assays targeting the small-subunit 18S ribosomal RNA gene are sensitive and specific for clinical detection.[6]
- Conventional and nested PCR assays targeting the 18S rRNA gene may be used in reference or research laboratories, particularly when sequencing or genotyping is required.
- Nested PCR should not be considered the sole or universal method of choice because real-time PCR and closed-system multiplex assays are now widely used.
- FDA-cleared multiplex gastrointestinal pathogen panels, including the BioFire FilmArray Gastrointestinal Panel, can detect Cyclospora cayetanensis together with other enteric pathogens.[9]
- The organisms included in multiplex panels vary; clinicians should confirm that the selected panel specifically includes Cyclospora.
- In solid-organ transplant recipients and other immunocompromised patients, guideline-supported diagnostic options include stool microscopy with modified acid-fast or safranin staining, ultraviolet autofluorescence, or a gastrointestinal multiplex molecular assay.[10]
The image below demonstrates a positive fecal specimen using a historical nested-PCR assay. The diagnostic band for Cyclospora cayetanensis is approximately 308 base pairs. This gel-based method is not the only current molecular diagnostic approach.
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Serological Testing
No validated, routinely available serologic assay is used for the clinical diagnosis of cyclosporiasis. Serologic or immunologic methods currently cannot provide a sufficiently specific diagnosis at the individual-patient level.[1][3]
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Giangaspero A, Gasser RB (2019). "Human cyclosporiasis". Lancet Infect Dis. 19 (7): e226–e236. doi:10.1016/S1473-3099(18)30789-8.
- ↑ 2.0 2.1 2.2 2.3 2.4 Miller JM, Binnicker MJ, Campbell S; et al. (2024). "Guide to utilization of the microbiology laboratory for diagnosis of infectious diseases: 2024 update by the Infectious Diseases Society of America and the American Society for Microbiology". Clin Infect Dis. doi:10.1093/cid/ciae104.
- ↑ 3.0 3.1 Pyzocha N, Cuda A (2023). "Common intestinal parasites". Am Fam Physician. 108 (5): 487–493.
- ↑ Shane AL, Mody RK, Crump JA; et al. (2017). "2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea". Clin Infect Dis. 65 (12): e45–e80. doi:10.1093/cid/cix669.
- ↑ Ortega YR, Sterling CR, Gilman RH, Cama VA, Díaz F (1993). "Cyclospora species—a new protozoan pathogen of humans". N Engl J Med. 328 (18): 1308–1312. doi:10.1056/NEJM199305063281804. PMID 8329770.
- ↑ 6.0 6.1 Qvarnstrom Y, Benedict T, Marcet PL; et al. (2018). "Molecular detection of Cyclospora cayetanensis in human stool specimens using UNEX-based DNA extraction and real-time PCR". Parasitology. 145 (7): 865–870. doi:10.1017/S0031182017001925.
- ↑ 7.0 7.1 Centers for Disease Control and Prevention. "DPDx—Cyclosporiasis". Retrieved July 10, 2026.
- ↑ Visvesvara GS, Moura H, Kovacs-Nace E, Wallace S, Eberhard ML (1997). "Uniform staining of Cyclospora oocysts in fecal smears by a modified safranin technique with microwave heating". J Clin Microbiol. 35 (3): 730–733. doi:10.1128/JCM.35.3.730-733.1997. PMID 9041420.
- ↑ Buss SN, Leber A, Chapin K; et al. (2015). "Multicenter evaluation of the BioFire FilmArray gastrointestinal panel for etiologic diagnosis of infectious gastroenteritis". J Clin Microbiol. 53 (3): 915–925. doi:10.1128/JCM.02674-14. PMID 25588652.
- ↑ La Hoz RM, Morris MI, AST Infectious Diseases Community of Practice (2019). "Intestinal parasites including Cryptosporidium, Cyclospora, Giardia, and Microsporidia, Entamoeba histolytica, Strongyloides, Schistosomiasis, and Echinococcus: guidelines from the American Society of Transplantation Infectious Diseases Community of Practice". Clin Transplant. 33 (9): e13618. doi:10.1111/ctr.13618.