Ova and Parasite exam (O&P)
Detection of the presence of parasites in a stool specimen
Bacteria, viruses and parasites individually and collectively are infectious causes of both acute and chronic diarrhea. For all patients with infectious diarrhea on the differential diagnosis, stool specimens are tested at PHML using the gastrointestinal multiplex PCR panel (GIPP) that detects the most common bacterial, viral and parasitic pathogens*.
When parasitic infection is considered as the differential diagnosis in the appropriate clinical context, the specimen is initially tested by GIPP which detects the following protozoa: Giardia spp., Cryptosporidium spp., Cyclospora cayetanensis, Dientamoeba fragilis and Entamoeba histolytica.
Any additional parasite testing that includes microscopic examination of the liquid stool will be performed at an out-of-province reference laboratory.
In order to refer out specimens for additional O&P microscopy, the following criteria must be met:
GIPP test is NEGATIVE
History of diarrhea greater than 14 days
AND at least ONE of the clinical criteria below:
- Relevant travel history
- Recent Immigrant/refugee to Canada (generally within 6 months of arrival)
- Immunocompromised host (i.e. transplant, cancer, HIV/AIDS, on biological therapy or chronic immune suppressive medications such as steroids)
Please consult the Microbiologist on Call (MOC) if a GI parasitic infection is suspected or high on your differential diagnosis if the above criteria are not met.
The diagnosis of pinworm (Enterobius vermicularis) is established by microscopic examination of sample collected using alternative techniques such as pinworm collector paddle applied directly on anal mucosa, as pinworms are not routinely found on stool examination. If pinworm is suspected please refer to acceptable specimens section for information on collection kits and collection procedure.
To facilitate timely testing, all health care providers requesting O&P test are required to indicate relevant clinical information and history on the requisition to avoid delay of test processing.
If appropriate clinical criteria or clinical history is NOT communicated to the laboratory upon receipt of the specimen, the liquid stool will NOT be referred out of province for O&P testing and the laboratory report will specifically outline this.
*PCR panel includes: Salmonella spp., Shigella/Enteroinvasive E. coli, Shiga-toxin producing E. coli, Enteropathogenic E. coli, Enterotoxigenic E. coli, Enetroaggregative E. coli, Campylobacter spp, Yersinia enterocolitica, Clostridiodes difficile, Rotavirus A, Norovirus I/II, Adenovirus, Sapovirus, Astrovirus, Giardia spp., Cryptosporidium spp., Cyclospora cayetanensis, Dientamoeba fragilis, Entamoeba histolytica.
Ova and Parasite exam
Ova and Parasite
If O&P testing is ordered, please collect stool in both sodium acetate-acetic acid-formalin (SAF) transport media AND stool transport container (i.e. Cary Blair medium). Both containers must be received by PHML when stool O&P is ordered. Order both GIPP and OVAP mnemonics in Meditech or indicate on requisition for both tests.
· Fecal specimens should be collected prior to administration of antibiotics and anti-diarrhea medications. Avoid use of barium, bismuth and mineral oil as these substances may interfere with the detection and identification of intestinal parasites.
· Collect stool in a clean, dry container. Immediately transfer a small amount of stool to the SAF container until the fluid reaches the fill line. Use any areas of the stool appearing bloody, slimy or watery. Mix stool with SAF until smooth.
For pinworm, early morning perianal samples should be collected using Pinworm Collector Paddles that may be ordered from the PHML Supply Store at 709-777-7123 or 709-777-6415 or by ordering on the publichealthlab.ca website. Pinworm Collector Paddles should be shipped to PHML at room temperature and received within 48hrs of collection.
Specimen Storage/Transportation Requirement
|Specimen||Minimum Volume||Room temperature||Refrigerated||Frozen|
|Stool in SAF||Add stool to “fill line” only.||YES||NO||NO|
|Stool in transport container (i.e. Cary Blair medium).||0.5ml stool||NO||YES 1||YES 2|
- If stool in Cary Blair transport medium CANNOT be immediately shipped to PHML, please store at 2-8ºC if delivery will be within 72 hours
- Freeze and ship frozen (-20ºC) if shipment will be delayed or will take over 72 hours.
Reject Due To
· Specimens not meeting the criteria listed in TESTING ALGORITHM. Please consult the Microbiologist on Call if a GI parasitic infection is suspected or high on your differential diagnosis and the above criteria are not met.
· No SAF stool received.
· Stool received only in SAF, no transport container such as Cary Blair.
· Leaking or inappropriately labelled sample containers will NOT be accepted.
· Stool specimen for pinworm investigation which is not submitted on pinworm paddle.
Detection of the presence of parasites in a stool specimen when parasitic infection is considered as the differential diagnosis in the appropriate clinical context.
Diarrhea is defined by increased stool frequency, liquidity, or volume, typically at least three times watery/ unformed stools in a 24-hour period which is new or unusual for the patient. According to the duration of symptoms, diarrhea is categorized into acute diarrhea (<2 weeks duration), persistent diarrhea (2-4 weeks duration) and chronic diarrhea (> 4 weeks duration).
Acute diarrhea typically is self-limited and does not require stool testing unless in the presence of certain clinical or epidemiological features, such as age >65 years, pregnancy, immune compromise, volume depletion, hematochezia (blood-tinged stool), fever, severe abdominal pain, known or suspected inflammatory bowel disease, community infectious disease outbreaks, need for hospitalization and employment as a food handler.
Persistent and chronic diarrhea presents a broad differential diagnosis, including infectious and non-infectious etiologies. Common non-infectious causes are irritable bowel syndrome, inflammatory bowel disease, malabsorption syndromes such as lactose intolerance and celiac disease, etc. Infectious agents may be bacterial (C.difficile, Salmonella, Aeromonas, Pleisiomonas, Yersinia, and Mycobacteria) or parasitic (amoebiasis, Strongyloides stercoralis, Schistosoma, Trichuris trichuria, Giardia, Cryptosporidium, Cyclospora, Isospora as well as microsporidium in immunocompromised population).
Stool microscopy for ova and parasites (O&P) has its highest clinical utility when guided by detailed medical history (food history, residence, occupational exposure, recent and remote travel, pets, and hobbies, etc.) and comprehensive physical examination.
Most helminths do not cause diarrhea; for cases in which helminth infection is suspected, both gross evaluation (for proglottids, larvae, or adult worms/worm fragments) and microscopic evaluation (for eggs and larvae) are appropriate.
The diagnosis of pinworm (Enterobius vermicularis) is established by microscopic examination of sample collected using alternative techniques such as pinworm collector paddle applied directly on anal mucosa, as pinworms are not routinely found on stool examination
NO OVA CYSTS AND PARASITES DETECTED
Leber, A. L., and Novak-Weekley, S. 2007. Intestinal and Urogenital Amebae, Flagellates, and Ciliates, p. 2092-2112. In Murray, P. R., Baron, E. J., Jorgensen, J. H., Landry, M. L., and Pfaller, M. A. Manual of Clinical Microbiology, 9th ed., vol. 2. ASM Press, American Society for Microbiology, Washington, DC.
Ova, Cyst and Parasite (O&P exam)
Approved stool specimens are examined at PHOL. Please refer to https://www.publichealthontario.ca/en/laboratory-services/test-information-index/parasite-faeces for test performance
Anti-diarrheal medication, radiological dyes (barium) and antibiotics interfere with the identification of intestinal protozoa as well as helminths and coccidians.
Performing Laboratory Location
Public Health Ontario Laboratory