Early diagnosis of typhoid fever by an enzyme immunoassay usingSalmonella typhi outer membrane protein preparations

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Abstract
An enzyme immunoassay (EIA) for detection of serum antibodies in patients with typhoid fever was developed usingSalmonella typhi outer membrane protein (OMP) preparations as antigen. Acute phase (first week) sera from adult typhoid fever patients were tested as well as sera from the following control groups: adult travellers with diarrhea caused by enterotoxigenicEscherichia coli, children infected withCampylobacter jejuni, healthy Mexican adult blood donors, and adults with septicemia caused by other organisms. At a 1:3,125 serum dilution, the mean absorbance values were 1.41 in the typhoid fever patients, and 0.57, 0.55, 0.51 and 0.52 in the respective control groups. Inhibition EIA studies using OMP preparations or lipopolysaccharide (LPS) as free antigen indicated that proteins can play an important role in the detection of antibodies in early typhoid fever. This EIA may be useful for the diagnosis of typhoid fever since results were obtained within about five hours and in an endemic area antibodies againstSalmonella typhi OMP preparations appear early in the course of the disease.