From the Guidelines
The most effective approach to diagnosing parasitic infections involves a combination of stool examinations, blood tests, and specialized diagnostic procedures, with the choice of tests depending on the suspected parasite, patient symptoms, travel history, and exposure risk. According to the most recent guidelines 1, the primary method of diagnosis is stool analysis, which involves direct microscopic examination of fecal samples for ova and parasites (O&P), often collected over multiple days to increase detection rates.
Key Diagnostic Tests
- Stool examinations: direct microscopic examination of fecal samples for ova and parasites (O&P)
- Blood tests: complete blood counts to check for eosinophilia (elevated eosinophils) and serological tests to detect antibodies against specific parasites
- Molecular diagnostic techniques: PCR offers higher sensitivity for detecting parasite DNA in samples
- Specialized tests: cellophane tape test for pinworm detection, antigen detection assays for parasites like Giardia lamblia and Cryptosporidium, and biopsies for tissue-dwelling parasites
Considerations for Testing
- Patient symptoms: gastrointestinal symptoms, fever, bloody or mucoid stools
- Travel history: recent travel to areas with high prevalence of parasitic infections
- Exposure risk: exposure to contaminated food or water, contact with infected individuals
- Immunocompromised status: broader differential diagnosis recommended, including testing for opportunistic pathogens like Cryptosporidium, Cyclospora, and Cystoisospora 1
Recent Updates in Guidelines
- Updates in the epidemiology of infections causing eosinophilia, with changes in the global prevalence of filarial infections 1
- New recommendations for empirical treatment of asymptomatic eosinophilia, including albendazole and ivermectin 1
- Review of parasitological tests available at national laboratories and updates on treatment options for various parasitic infections 1
From the Research
Laboratory Tests for Parasitic Infections
To diagnose parasitic infections, several laboratory tests can be employed. The choice of test depends on the suspected parasite and the clinical presentation of the patient.
- Stool Ova and Parasite Examination (O&P): This is a traditional method used to detect parasites and their eggs in stool samples 2, 3, 4, 5. However, it has been found that immunoassays are more sensitive for detecting certain parasites like Giardia and Cryptosporidium 2.
- Enzyme Immunoassays (EIAs): These are more sensitive than O&P for detecting Giardia and Cryptosporidium 2. EIAs can be used as an initial screening test, and O&P can be reserved for patients with negative EIA results and persistent symptoms or those at increased risk for non-Giardia, non-Cryptosporidium infection.
- Multiplex Real-Time PCR: This is a molecular test that can simultaneously detect multiple parasites, including Entamoeba histolytica, Giardia lamblia, and Cryptosporidium parvum, in fecal samples 6. This test offers high sensitivity and specificity and can improve patient management and infection control.
- Examination of Multiple Stool Specimens: Some studies suggest that examining multiple stool specimens can increase the detection rate of parasites 4, 5. However, others have found that examining a single specimen can be sufficient in most cases, especially when the prevalence of infection is low 4.
Recommendations for Laboratory Testing
Based on the available evidence, the following recommendations can be made:
- Use EIAs as the initial screening test for Giardia and Cryptosporidium.
- Reserve O&P for patients with negative EIA results and persistent symptoms or those at increased risk for non-Giardia, non-Cryptosporidium infection.
- Consider using multiplex real-time PCR for simultaneous detection of multiple parasites.
- Examine a single stool specimen in most cases, but consider examining multiple specimens in certain situations, such as when the prevalence of infection is high or when the clinical presentation is suggestive of a parasitic infection.