Choosing Wisely:

Don’t order a comprehensive stool ova and parasite microscopic exam on patients presenting with diarrhea lasting less than seven days who have no immunodeficiency or no history of living in or traveling to endemic areas where gastrointestinal parasitic infections are prevalent. If symptoms of infectious diarrhea persist for seven days or longer, start with molecular or antigen testing and next consider a full ova and parasite microscopic exam if other testing is negative.

Rationale and Comments: The comprehensive ova and parasite microscopic exam often requires submission of multiple stool samples, is labor intensive, requires significant expertise to perform, and typically has lower sensitivity when compared with many other tests now available. Instead, consider ordering antigen detection tests (i.e., direct fluorescent antibody, enzyme immunoassay, indirect immunofluorescence assay, rapid immunochromatographic tests), modified acid-fast stain, or molecular tests that detect specific gastrointestinal parasites most commonly acquired in the United States. When investigating cases of gastrointestinal disease, it is important to take a comprehensive clinical history that considers the patient’s exposure risk, mechanism(s) of transmission, and immune status. Patients lacking international travel history or residence in areas where parasites are endemic are most likely to be exposed to intestinal parasites associated with outbreaks from exposure to contaminated food or water. In the United States these pathogens include Giardia duodenalis (G. lamblia, G. intestinalis), Entamoeba histolytica, Cryptosporidium, and Cyclospora. For most individuals with healthy immune systems, symptoms self-resolve without treatment. Testing is recommended in individuals with prolonged symptoms, risk for development of severe infection, or when pathogen identification is necessary for public health reasons. Numerous antigen detection assays and molecular tests, including multiplex panels, have been developed for targeted detection of the most common gastrointestinal parasites acquired in the United States.
Sponsoring Organizations:
  • American Society for Clinical Laboratory Science
  • Sources:
  • IDSA guideline
  • Disciplines:
  • Gastroenterologic
  • Infectious disease
  • References: • Centers for Disease Control and Prevention. DPDx- Laboratory identification of parasites of public health concern. Stool specimens- detection of parasite antigens. Website accessed 23 May 2019.
    • Centers for Disease Control and Prevention. Parasites. Website accessed 23 May 2019.
    • Garcia LS, Arrowood M, Kokoskin E, et al. Practical guidance for clinical microbiology laboratories: laboratory diagnosis of parasites from the gastrointestinal tract. Clin Microbiol Rev. 2017;31(1):e00025-17.
    • Shane AL, et al. 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea. Clin Infect Dis. 2017;65:1963-1973.

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