Strongyloides – Serology

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

Background
This page provides routine serology (antibody) testing information for human strongyloidiasis at Public Health Ontario (PHO). The main causative agent of human strongyloidiaisis is Strongyloides stercoralis.

The test information described below is limited to serologic testing. For microscopy, please refer to Strongyloides stercoralis Faeces.

Updates

As of June 05, 2023, PHO’s laboratory has changed its Strongyloides serology assay from the SciMedx Strongyloides Serology Microwell ELISA (SciMedx Corp, Denville, US) to the EUROIMMUN Anti-Strongyloides IgG ELISA (EUROIMMUN AG, Luebek, Germany).
Turnaround time is reduced from up to 10 business days to up to 7 business days.

*Uncontrolled print copy. Valid only on day of print: 01 May 2024.

Testing Indications

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

Chronic strongyloidiasis screening for individuals with risk factors of progression to hyperinfection or disseminated diseases is strongly recommended. Indications for screening are described in the Committee to Advise on Tropical Medicine and Travel (CATMAT) guidelines.

Acceptance/Rejection Criteria

All requests meeting routine specimen collection and handling requirements (see below) will be accepted for testing.

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 Form, including:

Test(s) requested and indication for testing
Travel history (if applicable)
Clinical information including symptom onset date or if asymptomatic
Patient setting/population

Label the specimen container with the patient’s first and last name, date of collection and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or testing delay.

Limitations

Haemolysed, icteric, lipemic or microbially contaminated sera are not recommended for testing.

Storage and Transport

Centrifuge tube if using serum separator tube (SST). Place specimen in biohazard bag and seal.

Specimens should be stored at 2-8°C following collection and shipped to PHO’s laboratory on ice packs as soon as possible. All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Routine Strongyloides serology testing is performed at PHO’s laboratory up to 3 times per week (not available on weekends and holidays).

Turnaround time is up to 7 business days from receipt at PHO’s laboratory.

Turnaround for priority testing specimens is 48 to 72 hours from receipt at PHO’s Toronto laboratory site, depending on the day and time of receipt. Specimens that are requested as priority for next available run must be received at PHO by 1 p.m. before the day of testing.

STAT and Critical Samples Testing

Priority testing is reserved for individuals suspected of strongyloidiasis with moderate to severe COVID-19 infection considered for imminent life-saving immunosuppressive therapy (corticosteroids 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 provided further recommendations on Ivermectin to Prevent Disseminated Strongyloides Infection in Patients with COVID-19.
If priority testing is needed:

Notify PHO before sending a priority specimen by contacting our Customer Service Centre at 416-235-6556 / 1-877-604-4567.
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.
Clearly mark as “Priority” with the appropriate indication (e.g., COVID-19, immunosuppressive therapy, steroids, dexamethasone, tocilizumab, sarilumab, etc.) on the requisition.
Ship priority specimens directly to PHO’s Toronto laboratory 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.

Priority specimens will be tested on the next available run. Failure to follow the submission instructions above may result in testing delays.

Test Methods

Strongyloides serology testing is performed using a Health Canada licensed commercial enzyme-linked immunosorbent assay (ELISA), the EUROIMMUN Anti-Strongyloides IgG ELISA. The assay uses purified Strongyloides papillosus larvae antigen extracts to detect the presence of anti-Strongyloides IgG antibodies in serum. The assay provides a semi-quantitative value based on the ratio between the extinction of the control signal and extinction of the calibrator signal.

Performance and Limitations
When tested at PHO’s laboratory, the EUROIMMUN assay showed 96% positive percent agreement and 96% negative percent agreement compared to other ELISA assays, and improved analytical sensitivity and specificity compared to PHO’s previous assay. Buonfrate et al. (2021) reported a 91% sensitivity and 88% specificity compared to a composite reference standard¹.

Although not investigated with this assay, sensitivity with other Strongyloides ELISA tests has been reported as lower in acute infection (compared to chronic infection), travelers (compared to migrants), and individuals with impaired immunity^2,3. Cross-reactivity may occur with other helminth infections (including Schistosoma, Echinococcus, Toxocara, and filarial nematodes). Serology may remain positive after treatment but usually with decreasing signal values or seroreversion by 6 to 12 months⁴. Performance has not been evaluated for Strongyloides fuelleborni human strongyloidiasis infections.

Interpretation

Strongyloides serology interpretation table

Signal Ratio	IgG Result	Interpretation
<0.8	Non-reactive	No detectable level of IgG antibody against Strongyloides spp.
≥0.8 to <1.1	Indeterminate	Strongyloides spp. IgG antibody status inconclusive. Clinical and exposure correlation is required. Treatment and/or repeat testing may be advised depending on the patient’s risk status.
≥1.1	Reactive	Detectable level of IgG antibody against Strongyloides spp. Cross-reactivity may occur with other helminths including filarial nematodes, hookworms, Toxocara, Schistosoma, Trichinella, Ascaris, Taenia, and Echinococcus. Clinical and exposure correlation is advised, with further testing as appropriate.

Signal Ratio

IgG Result

Interpretation

<0.8

Non-reactive

No detectable level of IgG antibody against Strongyloides spp.

≥0.8 to <1.1

Indeterminate

Strongyloides spp. IgG antibody status inconclusive. Clinical and exposure correlation is required. Treatment and/or repeat testing may be advised depending on the patient’s risk status.

≥1.1

Reactive

Detectable level of IgG antibody against Strongyloides spp. Cross-reactivity may occur with other helminths including filarial nematodes, hookworms, Toxocara, Schistosoma, Trichinella, Ascaris, Taenia, and Echinococcus. Clinical and exposure correlation is advised, with further testing as appropriate.

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

References

Buonfrate D, Marrone R, Silva R et al. Prevalence of Strongyloidiasis in a Cohort of Migrants in Italy and Accuracy of a Novel ELISA Assay for S. stercoralis Infection, a Cross-Sectional Study. Microorganisms. 2021 Feb; 9(2): 401.
Dong MD, Karsenti N, Lau R et al. Strongyloidiasis in Ontario: Performance of diagnostic tests over a 14-month period. Travel Med Infect Dis. 2016 Nov-Dec;14(6):625-629.
Schaffel R, Nucci M, Carvalho E et al. The value of an immunoenzymatic test (enzyme-linked immunosorbent assay) for the diagnosis of strongyloidiasis in patients immunosuppressed by hematologic malignancies. Am J Trop Med Hyg. 2001 Oct;65(4):346-50.
Buonfrate D, Salas-Coronas J, Munoz J et al. Multiple-dose versus single-dose ivermectin for Strongyloides stercoralis infection (Strong Treat 1 to 4): a multicentre, open-label, phase 3, randomised controlled superiority trial. Lancet Infect Dis. 2019 Nov;19(11):1181-1190.