Comparison of serological and molecular Treponema pallidum tests in HIV patients in Kenya

Abstract

Background: Co-infection of HIV and Syphilis has profound impact in a patient. Syphilis infection is caused by Treponema pallidum. Two category of test methods are used; Nontreponemal test, e.g., RPR (rapid plasma regain) and Treponemal test such as TPHA (Treponema Pallidum Hemagglutination Assay). The current gold standard in Kenya/Nyeri is TPHA. Polymerase chain reaction (PCR) has higher sensitivity and specificity than serological assays.
Objective: To evaluate the test performance of serological methods (VDRL, RPR and TPHA) in syphilis testing using PCR as the gold standard among HIV patients visiting Nyeri county referral hospital.
Design: Cross-sectional study
Setting: Patients routinely attending the CCC clinic for antiretroviral treatment.
Subjects: 177 HIV patients receiving ARVs
Main outcome measures: Prevalence of syphilis, Test performances.
Interventions: Since TPHA performance has been shown to agree strongly with PCR, patient samples should be tested using TPHA to save time and cost with necessarily starting with VDRL or RPR
Results: The mean age of the study patients was 48.3 years with the majority 60.5% being female. The prevalence of syphilis was 18.6% by PCR. The sensitivity, specificity and kappa of tests were: RPR: 100%, 76.4% and kappa (0.546); VDRL: 100%, 55.6% and kappa (0.317); TPHA: 100%, 94.4% and kappa (0.864) and combination of RPR/VDRL and TPHA: 100%, 54.2%, and kappa (0.306).
Conclusion: The results show that neither RPR nor VDRL assay could be recommended as a stand-alone or as a confirmatory assay. The results of TPHA were the most concordant with those of PCR.