Dark ground microscopy and treponemal serological tests in the diagnosis of early syphilis.

OBJECTIVES: To evaluate the use of dark ground microscopy (DGM) and treponemal serological tests in the diagnosis of primary (PS) and secondary (SS) syphilis.
METHODS: A retrospective case note review of patients with early syphilis who attended our department between January 2001 and December 2002. Data were collected on demographics, results of treponemal serology and DGM.
RESULTS: 50 individuals had PS and 36 individuals had SS. DGM was performed in 31/50 (62%) of PS cases and this was positive in 97%. In 17 (34%) cases of PS, treponemal EIA was negative initially. DGM was performed on 13 of these, all of which were positive. Therefore, EIA had a sensitivity of 57% when compared to DGM. In 27 patients where EIA-IgM was performed, this was positive in 22 (81%), of which 12 were EIA negative on initial screening. All SS cases had positive EIA. DGM was performed in 19/36 (52%) of SS cases and was positive in 16/19--that is, a sensitivity of 84% when compared to EIA. The major reason why DGM was not performed in the cases of PS was that herpes was the presumed diagnosis and in SS the rash was attributed to other causes.
CONCLUSIONS: DGM is a rapid and sensitive test while EIA takes time for results and is less sensitive in PS. EIA-IgM is a useful adjunct in PS. DGM allows immediate diagnosis, treatment, and partner notification preventing further transmission. Genitourinary medicine clinics should have trained staff to perform DGM on all anogenital ulcers and suspected syphilitic lesions.