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

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

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).

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.

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.

0

2,000

4,000

6,000

8,000

10,000

Time of Storage (days)

AC

T R

eadi

ng (r

lu)

4 C wet 504 C wet 4864 C wet 3923 C wet 5023 C wet 48623 C wet 3936 C wet 5036 C wet 48636 C wet 394 C dry 504 C dry 4864 C dry 3923 C dry 5023 C dry 48623 C dry 3936 C dry 5036 C dry 48636 C dry 39