Kinetics of the Human Antibody Response against Salmonella enterica Serovars Enteritidis and Typhimurium Determined by Lipopolysaccharide Enzyme-Linked Immunosorbent Assay

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Abstract
Two indirect enzyme-linked immunosorbent assays (ELISAs) were employed to measure levels of immunoglobulin G (IgG), IgM, and IgA antibodies against Salmonella in sera from 303 Danish patients diagnosed by fecal culture with either Salmonella enterica serovar Enteritidis or Salmonella enterica serovar Typhimurium infections. The ELISAs were based on serovar Enteritidis lipopolysaccharide (LPS) and serovar Typhimurium LPS. The antibody levels were assessed approximately 1, 3, 6, and 12 months after the onset of salmonellosis. Sera from 164 healthy blood donors were analyzed to establish cutoff values for each analysis. One month after the onset of symptoms, the sensitivities of the assays were 95% for patients recovering from a serovar Enteritidis infection and 89% for patients recovering from a serovar Typhimurium infection. Three months after the onset of symptoms, these values had decreased to 85% and 55%. At 6 months they were 62% and 40%, and at 12 months they were 40% and 16%, respectively. The specificities of the assays were 97% for the serovar Enteritidis LPS ELISA and 94% for the serovar Typhimurium LPS ELISA. The high values for both sensitivity and specificity make these two ELISAs useful for serodiagnoses of Salmonella infection shortly after the acute phase of the infection and of Salmonella -associated reactive arthritis, as well as for seroepidemiological studies. A mixed ELISA consisting of both antigens, i.e., serovar Enteritidis and serovar Typhimurium LPS, was developed as a diagnostic tool with very high values for both specificity and sensitivity.