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

Background : 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. Methods : 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). Results : 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. Conclusion : 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. Strongyloides stercoralis (Ss) is a nematode parasite threatening the lives of millions of people in the tropical and subtropical regions of the world. Because of its autoinfective potential, this parasite can live in its host for many years, producing larvae that mature into adult worms within the host without the need for reinfection. Diagnosis of this parasite is challenging, relying on the detection of larvae in stool. Alternatively, serology has been very useful through the detection of antibodies produced against this parasite. The present study evaluates the diagnostic performance of 2 new lateral flow tests (Strongy Detect Rapid Tests) in comparison with the now commercially available Strongy Detect ELISAs. We used stored serum samples from Ss positive individuals, healthy controls and subjects infected with other helminth parasites. These lateral flow assays were very accurate at identifying Ss-specific antibodies in samples known to have the infection. There was an excellent agreement between these new lateral flow tests and the commercially available ELISAs. The excellent performance of these new tests makes them good diagnostic tools for use at point of care and in laboratory settings. [ABSTRACT FROM AUTHOR]