Is dark-field microscopy still useful for the primary syphilis diagnosis in the 21ST century?

INTRODUCTION: Serological test for primary syphilis could be negative the first 5-15 days. The aim of this study was to evaluate the benefit of including dark field microscopy (DFM) in the diagnosis algorythm for primary syphilis. MATERIALS/METHODS: Patients attended to a sexual transmission diseases clinic of Madrid, from 2015 to 2019, for a genital ulcer with clinical suspicion of primary syphilis. They were tested for DMF and serological test (EIA/TPPA/RPR). RESULTS: Over the total amount of samples (806), 53.2% (429) were positive for DFM. Thus, the 48% of the 429 patients had negative serological test (EIA/RPR) of which the 77.6% were positive at TPPA. CONCLUSIONS: DFM allows primary syphilis early diagnosis, even without serological test. If no direct detection methods are available, for patients without history of syphilis, TPPA could help to diagnose primary syphilis.