| OBJECTIVEAvidity index (AI) in the diagnosis of syphilis role to evaluate and identify current infection and previous infection of Treponema pallidum.METHODApplication of AI measurement, that is used Treponema pallidum antibodies in the serum of syphilis infection patients were captured by the Treponema pallidum recombinant antigens, and then the lower-avidity antibodies were eluted with urea. Indirect Enzyme-Linked Immunosorbent Assay (ELISA) was used to detect Treponema pallidum IgG antibodies. Avidity index of treponema pallidum was calculated. The titer of syphilis reagin was determined by TRUST, ELISA was used to detect TP-IgM antibodies.RESULTSPast infection of non-treatment group,107 cases of syphilis, the AI was 75.3±11.9% (x±s), the lower limit of 95% confidence interval was 51.9%, below the cut-off may be considered as the current infection. In observation group (a) of high TRUST titrer the AI-positive rate was 60.9%(14/23); In observation group (b) of low TRUST titrer the AI-positive rate was 6.7%(3/45); the observation group (a) and the control group (c) or observation group (b) showed significant difference (x2= 47.91 or 21.05 respectively, both P<0.01). There was no significant difference (x2= 0.01, P> 0.01) between the observation group (b) and the control group (c). Observation group (a, b) all AI positive rate was 25.00% (17/68), and TP-IgM positive rate of 32.35% (22/68). There was no significant difference (x2= 0.353, P> 0.05) between the observation group(a and b) all AI positive rate and TP-IgM positive rate. CONCLUSIONEvaluation of detection of TP-IgG AI, The cut-off value was 51.9% to determine previous infection or current infection of syphilis. In observed group (a) of high-TRUST titer the AI was low,TP-IgM positive of the AI was low, the AI showed a close relationship with the state of TP infection. combined with TP-IgM determination. The AI is a good indicator for distinguish between current or previous syphilis infection. |
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