Enzyme-linked immunosorbent assays (ELISA) for the diagnosis of enteric fever

Serum samples from 10 patients with culture positive Salmonella typhi infection, 30 febrile non-typhoidal patients, and 22 healthy subjects were tested for both Salmonella common structural antigen (CSA) and antibody to pathogenic species of Salmonella. Serum, urine and stool specimens from these patients were used to detect Salmonella antigen(s). IgM anti-S. typhi lipopolysaccharide antibody gave the best discrimination between typhoid patients, febrile non-typhoidal cases, and healthy control subjects. The highest IgM titer was recorded in the acute phase of the illness. Antigen detection in serum was highly sensitive (87.5%) and specific (100%), and always occurred early in the acute phase of the illness. Detection of antigen in stool was highly sensitive (87.5%) and specific (96.6%), but it usually was not detected until 3 weeks after the onset of acute illness. Antigen detection in urine was less sensitive and specific compared with assays of stool and blood. The study provides good evidence that ELISA for detection of Salmonella CSA and antibody can aid in the diagnosis and confirmation of infections caused by Salmonella.