Evaluation of an Indirect Immunofluorescence Assay for Strongyloidiasis as a Tool for Diagnosis and Follow-Up

Abstract

The diagnostic accuracy of an indirect immunofluorescence antibody test (IFAT) for Strongyloides stercoralis at different serum antibody titers was evaluated. To assess diagnostic sensitivity, sera from 156 patients with known strongyloidiasis were collected. Negative control sera were obtained from a composite group of 427 subjects (blood donors and hospitalized patients). With an area under the receiver-operating characteristic plot of 0.98, the IFAT showed a high level of diagnostic accuracy for strongyloidiasis. An antibody titer of >1:20, with 97% sensitivity and 98% specificity, was identified as the diagnostic threshold with the best overall performance. Cross-reactions were evaluated with 41 additional samples from patients with other known helminth infections, and the IFAT detected low-titer positivity in only one subject with filariasis. A positive IFAT result at an antibody dilution of >1:80 was virtually 100% specific, with 71% sensitivity. To test the usefulness of the IFAT as a monitoring tool, the changes in specific-antibody titers after treatment in a group of 155 patients were evaluated. Seroreversion or a decrease in antibody titer of twofold or more was observed in 60% of the patients. Response to treatment was directly correlated to the initial antibody titer, and a baseline titer of >1:80 was identified as the best predictor of response. In conclusion, a positive IFAT result at an antibody dilution of >1:20 is the optimal cutoff for screening. A titer of >1:80, with virtually no false-positive result, is a reliable cutoff for a serological assessment of treatment efficacy and for inclusion in clinical trials.

Strongyloidiasis: A case with acute pancreatitis and a literature review

“…The next available diagnostic studies are serological tests (Table 3), which depend on the detection of the larval antigen or antibody generated in response to their antigens. Indirect immunofluorescence antibody test for Strongyloides stercoralis has been shown to have a sensitivity of 97% and a specificity of 98% [29] . ELISA to detect antibody against crude Strongyloides larva antigen has also been widely used, with sensitivity and specificity of 93% and 95% respectively [30] .…”

“…A newer technique of nucleic acid amplification named Loop-mediated isothermal amplification has been introduced but needs further validation [34] . Table 3 above summarizes the sensitivity and specificity of these various diagnostic tests available [28][29][30]32,34,35] . Invasive methods like endoscopy with duodenal aspirate or biopsy can also be used in patients with strong clinical suspicion of infection.…”

“…Stool smear 30% sensitivity for single stool sample [35] Simple test but insensitive Agar plate culture 90% sensitivity [28] Sensitive and simple But needs 2 d for results Health hazard to lab workers Serologic tests IFAT IFAT: 97% sensitivity and 98% specificity [29] Cross reactivity except with LIPS ELISA ELISA: 93% sensitivity and 95% specificity [30] Inability to differentiate past and current infection LIPS LIPS: 97% sensitivity and 100% specificity [32] Expensive Molecular tests PCR PCR: 99%-100% sensitivity and 15%-100% specificity [34] Low specificity with low parasite burden Expensive LAMP Not widely available ELISA: Enzyme Linked Immunosorbent Assay; IFAT: Indirect immunofluorescence antibody test; LAMP: Loop-mediated isothermal amplification; LIPS: Immunoprecipitation system; PCR: Polymerase chain reaction.…”

Fatal disseminated strongyloidiasis after kidney transplantation

“…The indirect immunofluorescence antibody test (IFAT) is another serological test, but it is technically more complex than ELISA and requires specialized personnel for antigen preparation and reading the results; however, compared to ELISA, it gives quantitative results 12 .…”

“…The sensitivity and specificity of IFAT is very high and cross-reactivity in subjects with other nematode infections is negligible 12 .…”