Comparison of methods for the detection of Treponema pallidum in lesions of early syphilis

Background: The clinical diagnosis of primary and secondary syphilis can be difficult because of the wide variability of lesions. The available laboratory tests (dark-field microscopy and direct fluorescent antibody) require specialized microscopes and skilled technicians, and serologic tests are insensitive in early infection. Methods: Dark-field microscopy and monoclonal antibody staining were compared to a new solid-phase enzyme-linked immunosorbent assay (Visuwell test) for detection of T. pallidum in lesion exudate of 188 patients with genital lesions. Results: Sixty-four patients (34%) had lesions of early syphilis diagnosed by either dark-field, monoclonal antibody staining, or both. The Visuwell test and dark-field examination were positive in 52 (81.3%) and 55 (85.9%) of the 64 patients, respectively, whereas the monoclonal antibody staining technique demonstrated the presence of T. pallidum in 59 (92.2%) of the 64 patients. The Visuwell test gave a negative result in 111 of 124 patients who had negative dark-field and direct fluorescent antibody test results (89.5% specificity). Conclusions: The Visuwell test is an alternative method for evaluating genital ulcers but is less sensitive and specific than existing tests.