Improved diagnosis of Strongyloides stercoralis using recombinant antigen-based serologies in a community-wide study in northern Argentina

Abstract

The serodiagnosis of Strongyloides stercoralis infection by enzyme-linked immunosorbent assays based on crude antigen (CrAg-ELISA), while useful, has been limited by the reliance on crude parasite extracts. Newer techniques such as the luciferase immunoprecipitation system assay (LIPS), based on a 31-kDa recombinant antigen (termed NIE) from S. stercoralis and/or the recombinant antigen S. stercoralis immunoreactive antigen (SsIR), or the NIE-ELISA have shown promise in controlled settings. We compared each of these serologic assays in individuals from both regions of the world in which S. stercoralis is endemic and those in which it is not. A comprehensive stool evaluation (sedimentation concentration, Baermann concentration with charcoal cultures, agar plate, and Harada-Mori) and four different serologic techniques using CrAg-ELISA or recombinant NIE-ELISA as well as LIPS using NIE alone or in combination with a second recombinant antigen (NIE/SsIR-LIPS) were compared among individuals with parasitologically proven infection (n = 251) and healthy controls from regions of the world in which the infection is nonendemic (n = 11). Accuracy was calculated for each assay. The prevalence of S. stercoralis infection was 29.4% among Argentinean stool samples (n = 228). Sedimentation concentration and Baermann were the most sensitive stool-based methods. NIE-LIPS showed the highest sensitivity (97.8%) and specificity (100%) of the serologic assays. The calculated negative predictive value was highest for both the NIE-LIPS and CrAg-ELISA (>97%) irrespective of disease prevalence. No cross-reactivity with soil-transmitted helminths was noted. NIE-LIPS compares favorably against the current CrAg-ELISA and stool evaluation, providing additional accuracy and ease of performance in the serodiagnosis of S. stercoralis infections irrespective of disease prevalence.

FIG. 1.

Comparison of receiver-operator characteristic (ROC) curves for all four serologic methods based on results from a selected group of sera from patients with parasitologically proven S. stercoralis infection (n = 101) and healthy North American subjects without a history of travel to an area of endemicity (n = 10). The area under the curve (AUC) for each technique was as follows: CrAg-ELISA, 0.986; NIE-ELISA, 0.922; NIE-LIPS, 0.933; and NIE-SsIR-LIPS, 0.977.

FIG. 2.

Distribution and median values of IgG antibody determined by crude antigen ELISA (a), recombinant NIE antigen (b), and luciferase immunoprecipitation system assay (LIPS) using NIE antigen (c) or NIE and SsIR antigens (d) in 261 samples classified according to geographic origin and stool analysis results. Cutoffs are indicated by horizontal lines for each technique. Error bars indicate median ± interquartile range (IQR) per group. Samples were stool positive from Argentina (n = 67), stool negative from Argentina (n = 161), CDC normal (n = 10), and stool positive from Australia (n = 23). The CDC normal group included noninfected North Americans without travel to areas of endemicity. P values were calculated using the Mann-Whitney U test (two tailed).

FIG. 3.

Distribution and geometric mean values of IgG antibody titers to crude antigen determined by ELISA (a) and NIE determined by luciferase immunoprecipitation system assay (LIPS) (b) for 228 study samples from Argentina classified according to serologic results and the presence or absence of hookworms in the stool analyses. The serologic cutoff is marked as a thin horizontal line. Geometric means per group are shown as thick horizontal lines. P values were calculated using the Mann-Whitney U test (two tailed).