From the Guidelines
Strongyloides diagnosis should be approached with a combination of clinical suspicion and laboratory testing, prioritizing serological testing with ELISA for anti-Strongyloides antibodies due to its higher sensitivity, especially in non-endemic areas 1.
Diagnosis Approach
The most direct approach is stool examination for larvae, but this has low sensitivity due to intermittent shedding, often requiring multiple samples.
- Stool examination may require the use of Baermann technique or agar plate culture to detect Strongyloides in stool 1.
- Serological testing with ELISA for anti-Strongyloides antibodies is more sensitive and commonly used, especially in non-endemic areas.
- Eosinophilia on complete blood count may provide a supportive finding but isn't specific.
Special Considerations
For patients with hyperinfection syndrome or disseminated disease, larvae may be detected in sputum, bronchoalveolar lavage fluid, or other body fluids.
- Molecular methods like PCR on stool samples are increasingly available with improved sensitivity.
- Duodenal aspiration or string test (Enterotest) can be used when other methods are negative despite strong clinical suspicion.
Importance of Early Diagnosis
Early diagnosis is crucial because immunosuppression (particularly with corticosteroids) can trigger potentially fatal hyperinfection syndrome in infected individuals.
- Testing should be considered for patients with unexplained eosinophilia, especially those with risk factors such as travel to endemic areas, rural residence, or agricultural occupation 1.
- The diagnosis is often made by serologic tests, and many experts recommend therapy for seropositive patients, despite negative stool examinations 1.
From the FDA Drug Label
Ivermectin is active against various life-cycle stages of many but not all nematodes. It is active against the tissue microfilariae of Onchocerca volvulus but not against the adult form. Its activity against Strongyloides stercoralis is limited to the intestinal stages Efficacy, as measured by cure rate, was defined as the absence of larvae in at least two follow-up stool examinations 3 to 4 weeks post-therapy. Concentration techniques (such as using a Baermann apparatus) should be employed when performing these stool examinations, as the number of Strongyloides larvae per gram of feces may be very low.
The diagnosis of Strongyloides infection is based on the presence of larvae in stool examinations. Stool examinations should be conducted using concentration techniques such as a Baermann apparatus to detect the larvae, as the number of larvae per gram of feces may be very low. At least three stool examinations should be conducted over three months following treatment to ensure eradication of the parasite 2.
From the Research
Strongloides Diagnosis Methods
- The diagnosis of strongyloidiasis can be challenging due to the low parasite load and irregular larval output, making conventional stool examination techniques ineffective in up to 70% of cases 3.
- Several immunodiagnostic assays have been developed, but they often show extensive cross-reactivity with other parasites, such as hookworms, filariae, and schistosomes 3.
- The enzyme-linked immunosorbent assay (ELISA) has been found to be a useful tool in diagnosing strongyloidiasis, particularly in patients with hematologic malignancies, with a sensitivity of 68% and a specificity of 89% 4.
- A rapid ELISA has also been evaluated and shown to have a sensitivity of 91.2% and a specificity of 93.3%, making it a valuable tool for diagnosis, especially in cases where stool examination is unrevealed or in patients at risk for severe clinical forms 5.
Comparison of Immunoassays
- A comparison of three immunoassays, including the InBios Strongy Detect IgG ELISA, the SciMedx Strongyloides serology microwell ELISA, and the luciferase immunoprecipitation system (LIPS) assay, found that they performed equivalently, but with moderate agreement with the LIPS assay 6.
- The study found that 65% of the samples demonstrated perfect agreement among the three assays, and the overall percent agreement of the InBios, SciMedx, and LIPS assays were comparable at 87.1%, 84.2%, and 89.1%, respectively 6.
Diagnostic Challenges
- The diagnosis of strongyloidiasis remains challenging due to the lack of sensitive and specific diagnostic tests, and the need for a combination of clinical evaluation and laboratory tests to confirm the diagnosis 3, 6.
- The use of immunodiagnostic assays should be carefully evaluated, as they may not be effective in detecting disseminated infections and may show cross-reactivity with other parasites 3, 6.