Wednesday, March 12, 2008
Commercially available assays that detect C. trachomatis (CT), N. gonorrhoeae (GC) and T. vaginalis (TV) DNA can detect dead organisms. While this advantage has enabled less restrictive sample collection and transportation methods to be implemented, it results in uncertainty in interpretation of test results following treatment. Few studies have evaluated the duration of DNA shedding following treatment in longitudinal cohorts.
To describe the duration of DNA shedding detectable by PCR following treatment for STI.
PCR (Roche COBAS Amplicor, Indianapolis) to detect CT, GC and TV DNA was performed on samples collected from adolescent women for 12 weeks following a clinic visit. The time to the first negative test result was calculated for those women that had no missing samples during the period of interest.
82 women enrolled in a larger study of adolescent sexual behaviors had CT infections that were treated immediately prior to collection of weekly swab samples; 38 women had GC and 42 had TV. The mean time in weeks to the first negative result (± s.e.) was 1.7 (± .15), 1.4 (± .20), and 1.4 (± .10), for CT, GC and TV, respectively. More than 92% of women had negative results by 2 weeks following treatment for GC and TV while >86% of women were negative for CT by the 2 week time point.
These estimates of time to negative results are likely to be conservative since samples were collected only weekly. It is probable that daily sampling would have resulted in even shorter periods until a negative result was obtained.
When patients seek testing two or more weeks following treatment, whether for continued symptoms or other concerns, negative results should be expected. For patients with positive results after this period of time, further investigation into possible causes (e.g. re-infection, treatment failure) is warranted.