Seroprevalence of syphilis by VDRL test and biological false positive reactions in different patient populations: Is it alarming? Our experience from a tertiary care center in India

INTRODUCTION: Many centers for sexually transmitted infections in India perform only a single screening assay for diagnosis of syphilis which may yield biological false positive (BFP) reactions. AIMS AND OBJECTIVE: The aim of this study was to determine the true picture of seroprevalence of syphilis and BFP reactions in different patient groups. MATERIALS AND METHODS: A total of 57,308 serial serum samples obtained over a period of 5 years from different patient groups were screened by venereal disease research laboratory (VDRL) test both qualitatively and quantitatively. VDRL reactive sera were confirmed by Treponema pallidum hemagglutination (TPHA) test. RESULTS: The overall seroprevalence of syphilis by VDRL test was 1.27%, and BFP rate in test population was 0.14%. The rate of BFP reactions among total tested male (0.44%) and female (0.1%) patients differs significantly. Out of 733 VDRL reactive samples, 81 were BFP, i.e., BFP reaction is occurring at a frequency of 11% of the total VDRL reactive samples (ratio of 8:1 for true positives/BFP). Similarly, among antenatal cases, almost 24% of the total VDRL reactive samples were BFP, or for every 116 true positives, there were 37 (almost one-third) BFP. CONCLUSION: Although the overall seroprevalence of syphilis is low; the frequency of occurrence of BFP reactions is quite alarming. Hence, treponemal test must be used for confirmation of VDRL reactive sera.