Performance of direct fluorescent antibody tests for routine diagnosis of Chlamydia trachomatis in Russian sexually transmitted disease clinics

Testing for Chlamydia trachomatis in Russia is usually done by microscopic examination of genital smears stained with fluorescent antibody provided in locally produced kits. The aim was to assess the sensitivity and specificity of such direct fluorescent antibody (DFA) tests compared with a nucleic acid amplification test (NAAT) (ligase chain reaction) to detect C. trachomatis in 171 cervical smears and 201 urethral smears from men. The patients were at high risk of chlamydial infection and had been recruited at three sexually transmitted disease clinics in Moscow. Among women, DFA test sensitivity was 6% (95% CI 0-14) and the specificity was 92% (95% CI 88-97). Among men, the sensitivity was 9% (95% CI 2-16) and the specificity was 90% (95% CI 83-94). Poor DFA test performance was probably due to poor antibody quality and such tests are not adequate for routine examination of populations with either low or high chlamydial prevalence. As there may remain a place for DFA testing where few patients are seen, the Russian Ministry of Health should enforce registration of diagnostic tests, and Russian manufacturers should seek ways of improving DFA test performance. However, the mainstay of testing should depend on NAATs.