Evaluation of a Particle Gel Immunoassay as a Screening Test for Syphilis

Abstract

Recent trends in Western Europe show an increase in sexually transmitted infections. Surveillance data in Switzerland confirm this rising trend. Notifications of syphilis cases nearly doubled in the year 2002 and almost tripled in 2003. This trend necessitates an early correct diagnosis making reliable screening tests mandatory. In the presented study a particle gel immunoassay (ID-PaGIA syphilis antibody test, Diamed) using recombinant treponemal antigens TpN15, TpN17 and TpN47 was evaluated as a screening test in comparison to the currently used Treponema pallidum particle agglutination test (Serodia-TPPA, Fujirebio). Serum samples were obtained from a cross-sectional sero-epidemiological study among men who have sex with men. Samples were tested with the PaGia and the TPPA. In the case of equivocal results a titrated TPPA of an external laboratory was used as a confirmation test. In total 650 serum samples (48 seropositive patients, 602 negative) were evaluated. The PaGIA showed a sensitivity of 0.89 (43/48) and the TPPA of 0.83 (40/48). This difference was not statistically relevant (p = 0.4). The particle gel assay showed a significantly higher specificity (1.0) compared to the TPPA (0.98) (p = 0.004). The PaGIA showed a sensitivity comparable to that of other treponemal tests with an even better specificity. Advantages of the PaGIA are the fast reaction time of only 20 min and the simplicity of the procedure with minimal technical equipment.