Verification of Wet Vs. Dry Simulated Vaginal Swab Samples After Mailing for Detection of C. Trachomatis and N. Gonorrhoeae

Background: Home collection of mailed vaginal swabs has been used for C. trachomatis (CT) and N. gonorrhoeae (GC) outreach screening.

Objectives: To verify the reliability of self-obtained vaginal swab specimens sent via US mail for CT and GC testing on dry- and wet-transported swabs.

Methods: CDC prepared inocula in sterile water to mock simulated vaginal swabs with dilutions ranging from 10⁷ to 1 IFU/ml of CT and 10⁷ to 10 CFU/ml of GC. Duplicate swabs were inoculated with 100ml of appropriate CT and GC dilutions. One swab was placed in the holding tube for dry transport and the other was placed into Gen-Probe transport media (“wet”). Individual specimens were placed in envelopes and sent via USPS to Johns Hopkins University laboratory. Upon receipt, the dry swabs were placed into Aptima transport media and all samples were tested according to the Aptima protocol.

Results: For CT, there were 2 swabs each of 10⁷, 10⁵, 10³, and 10 each of 10 and 1 IFU/ml. All paired dry and wet swabs were detectable for CT.  For GC, there were 2 swabs each of 10⁷, 10⁵, 10³, and 10 of 10 CFU/ml.  All paired dry and wet swabs were detectable for GC.

Conclusions: The Gen-Probe APTIMA Combo 2 assay was able to detect CT and GC on all dry and wet swabs after transport. Mailing did not affect the ability of the assay to detect low, moderate and high levels of CT and GC in dry swabs.

Implications for Programs, Policy, and/or Research: Self-obtained vaginal swabs collected at home and transported dry could be used for the diagnosis of CT and GC as mailing does not affect the detection ability of Gen-Probe Aptima Combo2 assay.