STABILITY OF SEEDED SWAB SPECIMENS FOR THE DETECTION OF CHLAMYDIA TRACHOMATIS IN THE GEN-PROBE APTIMA? TEST

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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 manufacturers 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 gt 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 gt84 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).