The diagnostic value of the ELISA-Ty test for the detection of typhoid fever in children.

A study on the reliability of an enzyme linked immunosorbent assay (ELISA) for the detection of typhoid fever, the ELISA-Ty test, was conducted, comprising 44 children suffering from bacteriologically confirmed typhoid fever based on the finding of a positive blood culture for Salmonella typhi, 44 children with fever caused by diseases other than typhoid fever based on the finding of negative culture of blood, urine and stool for S. typhi, and 120 healthy children as controls. This ELISA-Ty test measures the concentration of IgM and of IgG against S. typhi in serum. This test is an indirect ELISA test, based on a method that makes use of a mixture of OMPs (outer membrane proteins) in equal proportion serving as antigen, obtained from different strains of S. typhi which are prevalent locally, peroxidase goat antihuman IgG or IgM (Sigma) as conjugate and orthophenylenediamine (Sigma) as chromogen of the substrate. The result of the test was obtained through the assessment of the end product, using a micro ELISA reader (Behring) at wave length of 490 nm. The data revealed that the mean absorbent values found in children with typhoid fever, for IgM and IgG, were significantly higher (p < 0.05) when compared to those in children with non-typhoid fever as well as to those found in children of the control group. The results of this study confirm that the ELISA-Ty test has a high reliability for the detection of typhoid fever in children, based on the finding of a degree of diagnostic sensitivity as high as 95.45% and 90.91% for respectively IgM and IgG, a diagnostic specificity as high as 93.33% for IgM as well as for IgG, a high diagnostic efficiency (94.32% for IgM and 92.05% for IgG), a high diagnostic positive predictive value of 93.33% for IgM and 93.02% for IgG, high negative predictive values of 95.35% for IgM and 91.11% for IgG for use under clinical as well as under field conditions.