SEROLOGIC TESTING FOR REACTIVE ARTHRITIS

The objective of the study was to determine the sensitivity and specif icity of quantitative serum antibody response to Salmonella enteritidi s lipopolysaccharide (LPS) as a diagnostic test for post-Salmonella re active arthritis (ReA). In a single food-source outbreak of Salmonella enteritidis, serum was collected from dysenteric individuals with and without ReA at 6, 12, and 24 months post infection. Serum was also co llected from control patients with no prior exposure to Salmonella inf ection. Quantitative measurements of isotypic antibodies to Salmonella enteritidis LPS were performed by an ELISA. Sensitivity and specifici ty of quantitative isotypic antibody levels over time were plotted on receiver operator characteristic (ROC) curves. Serum IgG and IgA anti- LPS were found to be present in higher levels in the ReA patients than in controls. Using the optimal cutoff of 0.10 selected from an ROC cu rve, IgG anti-LPS is 88% sensitive and 94% specific, and IgA anti-LPS is 75% sensitive and 100% specific. We conclude that IgA anti-LPS is b oth sensitive and specific in distinguishing prior exposure to Salmone lla LPS in ReA patients compared to unexposed controls.