Recombinant Antigen-Based ELISA Evaluated for Syphilis

The etiological agent of syphilis, Treponema pallidum, cannot be cultured and there is no single optimal alternative test. Serological testing is the most frequently used approach in laboratory diagnosis of the disease.

Scientists at Sekisui Virotech (Rüsselsheim, Germany) compared their Treponema pallidum Screen ELISA with standard tests. These tests included the fluorescent treponemal antibody absorption (FTA-ABS, Zeus Scientific; Branchburg, NJ, USA) test, which is an indirect fluorescent antibody technique; the T. pallidum particle agglutination (TPPA, Fujirebio; Hoofddorp, the Netherlands) test, which is a qualitative assay for the detection of antibodies to T. pallidum in serum or plasma. The most relevant test used for comparison was the Trep-Sure ELISA (Phoenix Bio-Tech Corporation; Mississauga, ON, Canada).

To establish the sensitivity and specificity of the Virotech Screen, 421 serum samples from different panels of infected and non-infected patients, sera from seronegative pregnant women as well as international syphilis standard sera and panels were tested. In comparison to combined TPPA/FTA-abs tests, Phoenix Trep-Sure and Virotech Screen demonstrated a sensitivity of 100% and a specificity of 93.9% and 98.3%, respectively.

All samples of a well-defined syphilis serum panel were correctly identified by the Virotech test, whereas the Phoenix test identified two Treponema negative samples as equivocal. The Trep Sure test is approved by the US Food and Drug Administration (FDA; Silver Springs, MD, USA). Results of both ELISAs highly correlated with TPPA negative and positive samples. The analytical sensitivity of the Virotech Screen with international standards was determined at 0.02 IU/mL and 0.03 IU/mL, and was slightly superior to the Phoenix Trep-Sure.

The authors concluded that the Virotech Screen ELISA demonstrated good diagnostic sensitivity and specificity when evaluated as a screening test for syphilis among various patient populations, including samples with increased rates of false positive nontreponemal test results. The Virotech ELISA may be used in automatic analyzers as an alternative to the manual TPPA. However, the use of a confirmatory test remains a must in order to avoid false-positive results. The study was published in the May/June, 2013 issue of the journal Clinical Laboratory.

Related Links:
Sekisui Virotech
Zeus Scientific
Fujirebio