Enzyme-linked immunosorbent assay for detection of Salmonella typhi Vi antigen in urine from typhoid patients

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Abstract
Because typhoid fever continues to be a major cause of illness in many developing countries, there is a clear need for a sensitive and specific test that will permit rapid laboratory diagnosis of the disease. An enzyme-linked immunosorbent assay (ELISA) has recently been developed and tested, both in the laboratory and in a clinical situation, for its ability to detect Vi antigen in urine. The ELISA was capable of detecting as little as 1 ng of purified Vi antigen per ml in urine, compared with 100 ng/ml detectable by a previously tested coagglutination method. It could also detect antigen in urine diluted as much as 1:1,024 in normal urine. In tests of urine specimens from six stool culture-positive persons in a small typhoid outbreak in the United States, the ELISA detected antigen in specimens from four of the six patients. The ELISA also proved to be specific, giving no false-positive results for specimens from 50 persons who did not have typhoid fever. The apparent high sensitivity and specificity of this ELISA make it a promising test for rapid diagnosis of typhoid fever.