Recombinant antigen-based lateral flow tests for the detection of Strongyloides stercoralis infection

Strongyloidiasis is a serious public health issue affecting millions of people worldwide particularly in tropical and subtropical regions. The laboratory diagnosis of strongyloidiasis is often serologically based, typically by enzyme linked immunosorbent assays (ELISA). However, the use of these assays at the point of care requires significantly different approaches for serologic measurements. We sought to determine the diagnostic performance of 2 prototype lateral flow tests alongside the Strongy Detect ELISAs (IgG and IgG4) that uses a cocktail of 2 Ss-specific recombinant antigens, Ss-NIE and Ss-IR.

The diagnostic performance of the Rapid Diagnostic Tests (RDTs) and ELISAs was determined by using stored serum samples from 17 healthy volunteers, 77 individuals known to be stool positive for Strongyloides stercoralis (Ss), 44 Ss stool-negative individuals but positive for Loa loa (n=32), or other helminths (n=12) (hookworm infection, Schistosoma mansoni, or Wuchereria bancrofti). Concordance between the RDTs and ELISAs was calculated with the Cohen's kappa statistic (κ).

The sensitivity and specificity of the IgG RDT was 95% (95% CI; 87.84 to 98.64%) and 94% (95% CI; 84.99 to 98.30%) respectively. The IgG4 RDT showed a sensitivity of 86.5% (95% CI; 77.63 to 92.83%) with 100% (95% CI; 94.13 to 100%) specificity. The IgG-based ELISA showed 100% (95% CI; 95.6-100%) sensitivity and 96% specificity (95% CI; 91.7-98%), whereas the IgG4-based ELISA revealed a 90% (95% CI; 81-94.3%) sensitivity with 100% (95% CI; 97.8-100%) specificity. Concordance between the RDTs and the ELISAs was excellent with κ = 0.94 (95% CI; 0.88-1.0%) for the IgGs and κ = 0.89 (95% CI; 0.81-0.97%) for IgG4 assays.

Given the high degree of sensitivity and specificity of both the IgG- and IgG4-based RDT, either of these would be useful in assessing Ss seropositivity in population-based studies and in screening patients at the point of contact.