APTIMA CT Test Results of Dry vs. Wet Spiked Swabs Over Time

1. STABILITY OF SEEDED SWAB SPECIMENS FOR THE DETECTION OF CHLAMYDIA TRACHOMATIS IN THE GEN-PROBE APTIMA TEST J Schachter and J Moncada. University of California, San Francisco, USA BACKGROUND There are many potential uses of nucleic acid amplification tests (NAATs) that are hindered by the manufacturer’s strict transport and storage conditions for specimens (for example, in developed countries or for mailed samples). To see if dry swabs would be suitable for such uses we evaluated the stability of seeded swab specimens in the APTIMA Chlamydia trachomatis (ACT, Gen-Probe Inc. San Diego, CA) test. MATERIALS AND METHODS We inoculated Dacron swabs with 50 µl of titrated C. trachomatis (CT)isolates and PBS (negative control). The CT were cultured from trachoma patients in Ethiopia, and yielded approximately 16, 28 and 138 inclusions for isolate #39, #50 and #486, respectively. The seeded swabs were inserted into sterile tubes (dry group) and into APTIMA transport tubes (wet group). A total of 40 samples (10 of each isolate x3, and 10 negative controls) for each group were then stored at room temperature (23º C), in refrigerator (4º C) and in incubator (36º C). At day 0 and weekly through day 84, samples held at the three temperatures were tested by ACT according to the package insert. For the dry swabs, 1.0 ml of M4 medium (Remel Inc, Lenexa, KS) was added to the tube, vortexed, and 200 µl was transferred to an APTIMA tube for testing. APTIMA CT Test Results of Dry vs. Wet Spiked Swabs Over Time RESULTS The performance of the dry and wet swabs were similar, even though dry samples were more dilute (dry swabs were rehydrated, then 1/5 volume tested). The rlu readings for both groups remained relatively high (~8700 rlu) for 21 days with a ~35% signal reduction (to ~5500 rlu) observed by day 28. Samples were positive at day 84, with a slight drop in rlu between days 28 to 84. Results for specimens stored at 36º C were comparable to those stored at 4º C and 23º C. * Days 35, 42 and 49 samples not tested by ACT. ACT positive > 100 rlu. CONCLUSIONS The performance of the dry swabs were similar to the wet swabs, even though samples tested were more dilute (1/5 volume tested). Our results show that the APTIMA RNA target for CT is very stable. Specimens stored longer, and above the temperatures recommended in the package insert (60 days at 2-30ºC) were not compromised, and the CT target could be detected >84 days. These preliminary findings with seeded specimens extend Gaydos’ finding that dry swabs may be suitable for the Gen-Probe NAATs (JCM, 2002, 40(3):758-61). Further studies are needed with matched clinical specimens to confirm the relevance of these findings, but such specimens could have many practical uses (shipping specimens from remote field activities, use in QC panels, among others). * Trachoma isolates (C. trachomatis, serovars A, Ba) and negative (phosphate buffer saline). # Dacron swabs spiked with 50 µl of sample and placed into Aptima transport tubes. + Dacron swabs spiked with 50 µl of sample and stored dry (without media).