Evaluation of a rapid enzyme-linked immunosorbent assay for diagnosis of strongyloidiasis

Abstract

Diagnosis of strongyloidiasis using stool examination remains unsatisfactory due to the lack of sensitivity and fastidious techniques. In this work, we investigated the value of an anti-Strongyloides IgG enzyme immunoassay (EIA), using a panel of 207 sera retrospectively collected from patients with definitive diagnoses of strongyloidiasis (n=57), other helminthic infections (n=46), eosinophilia without parasitic infection diagnosis (n=54), and digestive disturbances following a tropical journey (n=30) and from 20 negative controls. By following a receiver operating characteristic (ROC) curve analysis, it was possible to optimize the test to reach a sensitivity of 91.2% and a specificity of 93.3%, with 92.8% of patients correctly classified. Considering the incidence of strongyloidiasis diagnosed in our own laboratory, the negative predictive value was calculated at 99.9%. In conclusion, this test is very rapid and easy to perform and may be valuable for diagnosis of strongyloidiasis both in cases where the infection is unrevealed by a parasitological stool examination and in patients at risk for severe clinical forms, such as patients receiving immunosuppressive therapy.

FIG. 1.

Box plot of data from five groups of sera tested using the IVD ELISA for anti-Strongyloides IgG antibodies. Diamonds represent minimum and maximum values, central rectangles span the first quartile to the third quartile, bars above and below the box correspond to the 5th and 95th percentiles, respectively, and medians are represented by circles. Dotted lines represent the cutoff values recommended by the manufacturer (OD, 0.2) and used following a ROC analysis (OD, 0.11).

FIG. 2.

ROC curve of cutoff values for the decision to diagnose strongyloidiasis on the basis of the OD value obtained with the IVD ELISA for anti-Strongyloides IgG antibodies.