Stability of Chlamydia trachomatis RNA after long-term biobank storage

Archived vaginal samples are frequently used in ancillary research projects, yet few studies have validated their use for nucleic acid amplification analysis after long-term storage. This study sought to examine the suitability of vaginal swab samples for Chlamydia trachomatis transcription mediated amplification analysis after up to 20 years of biobank storage.

Replication testing was conducted using a subset of vaginal swab samples originally obtained between May 1999 and June 2001 using the BD CultureSwab™ collection and transport system (Becton Dickinson, NJ) as part of the Gynecologic Infections Follow-Through (GIFT) study.¹ C. trachomatis DNA amplification was performed using an SDA Assay (Becton Dickinson, NJ), and residual specimens were frozen at −80° C. For the current study, specimens from 40 women who originally tested negative and 20 women who tested positive for C. trachomatis were re-tested by ribosomal RNA based transcription mediated amplification using the fully automated Panther system (Hologic, San Diego, CA, USA) by laboratory personnel masked to the original results. Cohen’s kappa coefficient (κ) was used to measure agreement between original and repeated C. trachomatis measurements.

There was a 97% concordance between C. trachomatis results. Of the 20 specimens that originally tested positive, 18 tested positive when reanalyzed. All 40 samples which were negative in the original study tested negative when reanalyzed. Agreement between original and replication testing was high (κ = 0.92, p<0.0001). Repeated testing yielded a high sensitivity (90%), specificity (100%), positive predictive value (100%) and negative predictive value (95%) for the original C. trachomatis classification. Specimen age ranged from 17.7 years to 19.7 years, and there was no difference in sample age between those which replicated and those which did not (median 19.0 years, both groups). These findings demonstrate that chlamydial ribosomal RNA is sufficiently stable for use in ancillary studies after long-term storage.