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Indian Journal of Medical Microbiology, Vol. 26, No. 2, April-June, 2008, pp. 199-200 Correspondence Prevalence of Syphilis and Biological False Positive Reactions in VDRL Test among Injecting Drug Users: A Preliminary Study Jindal N, Aggarwal A Department of Microbiology, Govt. Medical College, Amritsar, Punjab -143 001 Date of Submission: 26-Sep-2007 Code Number: mb08060 Dear editor, Injecting drug users (IDUs) are a population at increased risk of developing syphilis. In developing countries screening for syphilis is done by non-treponemal tests (VDRL/RPR). Asymptomatic persons and patients with atypical presentations require confirmation by treponemal tests like Treponema pallidum haemagglutination (TPHA). VDRL is a standardised, economical, sensitive and easy to perform test but one major problem with this test is that it is associated with false positive reactions. Foreign studies on IDUs have reported more than 10% incidence of false positive results. [1] There is paucity of similar studies in India. Therefore the present study was conducted to address this issue. Serum samples collected from 150 IDUs (April 2003-March 2005) were subjected to VDRL test by standard method. Samples reactive in VDRL test were then subjected to TPHA test (TPHA-200 Kit, Kentford, UK). The samples reactive in both the VDRL and TPHA tests were interpreted as positive for syphilis. Out of 150 serum samples tested, 6 (4%) were found to be reactive by VDRL test. The antibody titre was> 8 in two (R32; R128) and < 8 in the remaining four. TPHA test was reactive in 2(1.3%). These two TPHA reactive samples were also reactive in VDRL test in titre> 8. Therefore, the prevalence of syphilis in IDUs on the basis of positive VDRL and TPHA test was 1.3% (2/150). This is lower than the prevalence rates reported in studies carried out in Delhi (6.09%), [2] Germany (3.3%) and Bangladesh (23%). [3] The possible explanation for this could be the difference in the subgroup of population studied and the diagnostic tests employed. In addition, region, gender, ethnic factors and socioeconomic factors which influence the development of sexual behaviour do play a big role in the prevalence of syphilis. It has been reported that more than 10% of injecting drug users have false positive test results in titres> 8. [4] However, we observed false positive reactions in only 2.7% IDUs and that too in titre < 8. The present study thus shows that in our financially constrained set-up VDRL test can be reliably employed for screening of IDUs. However, studies on larger scale are required to reach exact conclusion. References
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