Strongyloides – Serology

*Uncontrolled print copy. Valid only on day of print: 22 March 2023.

Testing Indications

This test provides semi-quantitative detection of serum IgG antibodies to Strongyloides stercoralis, the major causative agent of human strongyloidiasis.

Strongyloides serology can be used (in addition to microscopic identification) to diagnose acute and chronic strongyloidiasis, as well as to monitor treatment response where applicable.

Serology can also be used to screen individuals with risk factors for developing Strongyloides hyperinfection and disseminated disease. Recommended screening indications are further described in the Committee to Advise on Tropical Medicine and Travel (CATMAT) guidelines.

Priority testing is reserved for individuals suspected of chronic strongyloidiasis with moderate to severe COVID-19 infection considered for imminent immunosuppressive therapy (corticosteroid and/or monoclonal antibody treatment). In the event that testing results are not available or delayed, empiric treatment may be indicated. The Ontario COVID-19 Science Advisory Table has provided further recommendations on Ivermectin to Prevent Disseminated Strongyloides Infection in Patients with COVID-19.

Update (January 28, 2022)

Priority testing indications and submission notes have been added to this information sheet.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Strongyloides serology, Strongyloides stercoralis serology, Strongyloidiasis serology	General Test Requisition	Whole blood or serum	5.0 ml whole blood or 1.0 ml serum	Blood, clotted - Vacutainer tube (SST)

Submission and Collection Notes

Complete all fields of the General Test Requisition, including symptoms and onset date where applicable.

For priority testing of individuals with risk factors of strongyloidiasis and moderate to severe COVID-19 infection considered for immunosuppressive therapy:

Notify PHO before sending a priority specimen by contacting our Customer Service Centre at 416-235-6556 / 1-877-604-4567.
Clearly mark as “Priority” with the appropriate indication (e.g., COVID-19, immunosuppressive therapy, steroids, dexamethasone, tocilizumab, sarilumab, etc.).
Ship priority specimens separately from routine specimens in a clearly marked package (in accordance with the Transportation of Dangerous Goods Regulations) indicating “Priority” for easier retrieval.
Ship priority specimens directly to PHO’s laboratory Toronto site to the shipping and receiving dock at 661 University Ave., Toronto, Ontario. For delivery instructions please see Directions to 661 University Shipping Dock for Clinical Samples.
Failure to follow the submission instructions above may result in testing delays.

Grossly haemolysed, icteric, lipemic or microbially contaminated sera and specimens with fungal growth will not be tested.

Limitations

Cross-reactivity may occur with other helminths including Schistosoma, Echinococcus, Toxocara, and filarial nematodes. Clinical and exposure correlation is advised, with further testing as appropriate.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Routine Strongyloides IgG serology is performed once per week. Turnaround time is up to 10 days from receipt by PHO’s laboratory.

Priority testing is currently available on Mondays, Wednesdays, and Fridays (not available on weekends and holidays). The target turnaround time is 24 to 72 hours from receipt at PHO’s laboratory Toronto site, depending on the day and time of receipt. Specimens that are received by 1 p.m. on the day of testing will be included in the day’s run, otherwise the specimens will be tested on the next available run.

Test Methods

Strongyloides stercoralis IgG serology testing is performed using the Health Canada-licensed commercial SciMedx IgG enzyme-linked immunosorbent assay (ELISA) kit (SciMedx Corporation, Denville, NJ). Optical density (OD) reading of the signal intensity is also provided.

Interpretation

Results should be interpreted in the context of clinical and exposure history.

A non-reactive result (OD < 0.2) suggests no detectable level of antibody against Strongyloides stercoralis.

An indeterminate result (OD between 0.2 to 0.3) provides an inconclusive interpretation, and clinical/exposure correlation is required. Treatment and/or repeat testing may be advised depending on infection risk status.

A reactive result (OD > 0.3) suggests detectable level of antibody against Strongyloides stercoralis. Cross-reactivity may occur with other helminths including Schistosoma, Echinococcus, Toxocara, and filarial nematodes. Clinical and exposure correlation is advised, with further testing as appropriate.

Reporting

Results are reported to the ordering physician or health care provider as indicated on the requisition.

Performance Characteristics

Evaluation of the SciMedx assay used in Ontario was performed by Dong et al. (2016), and showed a 92% sensitivity and 88% specificity compared with the US Centers for Disease Control and Prevention (CDC) in-house EIA. Performance may vary depending on the stage of infection (e.g., acute vs. chronic).