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A transcription
mediated DNA amplification assay (TMA) for the detection of C.
trachomatis DNA in urine samples is sensitive when tested on
pools of 4 samples.
Sensitivity evaluation
of the Gen-Probe AMP-CT assay by pooling urine samples for the screening
of Chlamydia trachomatis urogenital infection.
Gomes JP, Viegas S, Paulino A, Catry MA.
Inter J STD
AIDS. 2002;13:540-542.
Summary:
Question
What is the sensitivity of pooled urine samples compared to individual
testing for the detection of C. trachomatis by a DNA amplification
assay?
Design
This study describes a comparison of the sensitivities of testing two
sample pool sizes, 4-fold and 8-fold, with testing of individual urine
samples for the detection of C. trachomatis DNA using a DNA
amplification assay.
Participants
The samples consisted of 264 first-catch urine samples from men and women.
Thirty-three samples were previously tested and found positive by PCR (Amplicor
C. trachomatis PCR assay, Roche Diagnostic Systems) and 231 were
freshly collected and untested.
Description of Tests and Diagnostic
Standard
All urine samples were prepared for analysis and tested individually using
the AMP-CT TMA assay according to the manufacturer's instructions
(Gen-Probe). Forty l of the solubilized pellets were used to make the
sample pools. An aliquot from each of the 33 known PCR-positive samples
was added to 33 tubes in duplicate. An aliquot from 3 other samples was
added to each of two tubes to make up 33 duplicate pools of 4 samples. An
aliquot of 4 additional samples was added to each tube in one set of 33
pools to make up 33 pools of 8 samples. Fifty l from each individual or
pooled sample was tested with the TMA assay. Freshly collected urine
samples that were positive by TMA were tested by PCR (Amplicor C.
trachomatis PCR assay, Roche Diagnostic Systems). True positive
samples were defined as those positive by both PCR and TMA.
Main Outcome Measures
The test results of the samples tested in pools of 4 or 8 were compared to
the results of samples tested individually.
Main Results
Thirty of 33 known PCR positive urine samples, and 4 of 231 fresh,
untested samples were positive by TMA when tested individually. The three
samples positive by PCR and negative by TMA yielded positive results by
TMA after 1:4 and /or 1:8 dilution with buffer. The 4 TMA positive fresh
samples were confirmed positive by PCR. Therefore, individual testing
detected 34 of 37 (91.9%) positive samples. Thirty-one of the 33 pools of
4 samples, and 28 of the 33 pools of 8 samples, each containing at least
one positive sample, were positive by TMA. Each TMA negative pool
contained only one positive sample. The 4X pooling strategy detected 33 of
35 (94.3%) and the 8X pooling strategy detected 32 of 37 (86.5%) positive
samples.
Authors' Conclusions
A four-fold pooling strategy for testing
urine samples by TMA may be useful for population based C. trachomatis
screening programs.
Source of funding: bio-Merieux-Portugal.
For correspondence: J. P. Gomes,
Centro de Bacteriologia, Instituto Nacional de Saude, Av. Padre Cruz,
1649-016-Lisboa, Portugal. E-mail address: j.paulo.gomes@insa.min.saude.pt
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