Epidemiology of strongyloidiasis determined by parasite-specific IgG detections by enzyme-linked immunosorbent assay on urine samples using Strongyloides stercoralis, S. ratti and recombinant protein (NIE) as antigens in Northeast Thailand

Abstract

Detection of anti-Strongyloides IgG in urine by enzyme-linked immunosorbent assay (ELISA) for diagnosis of strongyloidiasis reportedly has comparable performance to conventional serum assays. Initial comparisons of urine assays using commercial ELISA kits designated for serology have shown its diagnostic potential but sub-optimal accuracy. In the present study, we optimized urine ELISA protocols based on different antigen types and evaluated their accuracies in determining the epidemiology of strongyloidiasis in Northeast Thailand. Paired urine and fecal samples of 966 individuals from the study community were collected for three consecutive days and tested for strongyloidiasis. We compared three ELISA protocols using different antigens including crude S. stercoralis antigen (Ss-ELISA), crude S. ratti antigen (Sr-ELISA) and recombinant NIE antigen (NIE-ELISA) and fecal examination by agar plate-culture (APCT) technique and formalin-ethyl acetate concentration technique (FECT). The optimized ELISA protocols using three different antigen sources yielded significantly higher prevalence rates of strongyloidiasis (58.9-65.1%) than those by fecal examination methods (19.7%). The prevalence of strongyloidiasis determined by ELISA protocols significantly increased with age (p value < 0.0001) and males had higher prevalence than females (p value < 0.0001). Diagnostic agreements between ELISA protocols were moderate (κ = 0.461-0.586) and the agreement between each ELISA protocol and fecal examinations were slight (κ = 0.139-0.210). The results obtained by urine ELISA protocols using three different antigens showed comparable diagnostic performances, provided further supports for the utility of urine as an alternative clinical specimen for diagnosis of strongyloidiasis.

Fig 1. Daily and cumulative prevalence rates of Strongyloides infection according to fecal examination and urine ELISA methods (n = 966).

Panel A shows the prevalence rates for each of three successive days (D1: day1, D2: day2, D3: day3). Panel B shows the cumulative prevalence rate for three days (D1: day1, D2: day 1 and 2, D3: day 1, 2 to day 3). The small letter symbols (a-l) represent the McNemar’s chi-square value for a statistical comparison between pairs of prevalence estimates with p value < 0.0001; a = 66, b = 44, c = 28, d = 106, e = 38, f = 77, g = 130, h = 101, i = 35, j = 151, k = 109, and l = 47.

Fig 2

Prevalence profiles of S. stercoralis infection determined by different diagnostic methods arranged by age (Panel A) and gender (Panel B). * Stands for p value < 0.0001 obtained by chi-square test.

Fig 3. Distribution of anti-Strongyloides IgG levels among individuals with various parasitic infections determined by fecal examination.

Urine analysis protocols by Sr-ELISA (A), Ss-ELISA (B), NIE-ELISA (C). Points shown (dots) are individual values of IgG antibody (units/mL of urine). The long horizontal lines indicate the cut-off values of IgG level. Labels for parasitic infections; Ss: S. stercoralis, Ov: O. viverrini, Hw: hookworms, Bh: B. hominis, Gl: Giardia duodenalis, and EN: endemic negative. Short horizontal lines indicate means with lower and upper 95% confidence intervals.