Figure 4. Effect of sample storage on rat fecal supernatant and detection of heterologous S. stercoralis coproantigen.

(A) Pooled uninfected rat fecal supernatant collected from 6 rats (nRFS) and infected rat fecal supernatant (iRFS) collected from two rat (13 and 21 dpi) had previously been stored at −20°C and consistently tested negative and positive, respectively. Numbered samples 123, 150, 151, 160 and 161 represent samples collected from rats infected with known amounts of S. ratti infective larvae. Extracted fecal supernatant stored at 4°C displayed erratic absorbance values, as fecal supernatants from both uninfected and infected rats test positive. All unprocessed S. ratti infected feces stored in formalin (4% or 10%) tested positive for coproantigen when extracted after storage. Uninfected rat fecal feces tested negative when stored unextracted. All points are mean ± SEM of OD values obtained from duplicate samples. (B) Uninfected human fecal supernatant (nHFS) and Strongyloides-infected human fecal supernatants collected daily from a single patient with clinically diagnosed strongyloidiasis (SS01-SS03) were extracted simultaneously with 4% formalin and 10% formalin. All points are mean ± SEM. Assay cuttoff for negative reading is represented by the grey box.