Evaluation of the SsIR/NIE recombinant antigen ELISA for the follow up of patients infected by Strongyloides stercoralis – a diagnostic study

Abstract
Some serology assays demonstrated useful for post-treatment monitoring of Strongyloides stercoralis
infection. Serology frequently has low specificity, which might be improved by the use of
recombinant antigens. The Strongy Detect ELISA is based on two recombinant antigens (SsIR and
NIE) and proved good accuracy. Aim of this study was to evaluate the performance of this test for
the post-treatment monitoring of strongyloidiasis. We tested 38 paired sera, with matched fecal tests
results, stored in our biobank and originating from a randomized controlled trial. At baseline, all
patients tested positive for at least one fecal assay among PCR, direct stool microscopy and agar plate
culture. Patients were re-tested with both serology and fecal assays 12 months after treatment.
Primary outcome was the relative reduction in optical density (OD) between baseline and follow up.
We observed that about 95% samples showed a reduction between pre and post-treatment OD, with
a median relative reduction of 93.9% (IQR 77.3% - 98.1%). In conclusion, the test proved reliable
for post-treatment monitoring. However, some technical issues, including that the threshold for
positivity has not be predefined, and that a substantial number of samples showed overflow signals,
need to be fixed to permit use in routine practice.
Key words
Strongyloides; strongyloidiasis; ELISA; serology; follow up