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Urethral swabs and first-catch urine specimens for the detection of Chlamydia trachomatis were collected from 370 black men with urethritis who attended a sexually transmitted disease (STD) clinic in Pretoria. An enzyme immunoassay (EIA) for C. trachomatis was carried out on all urethral swabs and urine specimens. Chlamydial culture and a direct immunofluorescent antibody (DFA) test (Imagen, Dako, UK) were also carried out on urethral swabs; DFA was used for confirmation of urine EIA positives.
Based on culture and/or DFA, C. trachomatis was detected in 96 (26%) urethral swab specimens. The sensitivity of urine EIA investigation was 94% and the specificity 99%, compared with those of urethral swab EIA which. were 97% and 99% respectively. The positive and negative predictive values for urine were 96% and 98% compared with 96% and 99% respectively for urethral swabs. Urine examination was therefore sensitive and specific compared with urethral swab examination in these STD patients. In view of this, the advantage of urine as an alternative to urethral swabs for C. trachomatis detection is that sampling is non-invasive and non-traumatic.