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A strand displacement
amplification assay is a sensitive, specific, and efficient method for the
screening of urine samples for N. gonorrhoeae.
Evaluation of a strand
displacement amplification assay (BD ProbeTec-SDA) for detection of Neisseria
gonorrhoeae in urine specimens.
Akduman D, Ehret JM, Messina K,
Ragsdale S, Judson FN.
Journal of Clinical Microbiology 2002;40:281-283.
Summary:
Question
How well does the BDProbeTec-SDA system perform compared to culture for
the screening of large numbers of samples for the presence of N.
gonorrhoeae?
Design
This study describes a blinded comparison of the BDProbeTec-SDA assay
performed on urine samples with culture of endocervical or urethral swabs
and evaluation of the reproducibility of repeat analysis by the SDA assay.
Participants
Men and women (n = 3544) attending the Denver Metro Health sexually
transmitted disease clinic were studied.
Description of Tests and Diagnostic
Standard
Urine specimens from men and women were analyzed by the semi-automated BD
ProbeTec-SDA strand displacement assay (Becton Dickinson Microbiology
Systems, Sparks, MD) according to the manufacturer's instructions.
Amplification controls were used in each assay to monitor inhibition. The
SDA was repeated twice on all positive samples and 280 negative samples.
Matched endocervical swabs from women and urethral swabs from men were
cultured on modified Thayer-Martin and chocolate agar biplates.
Main Outcome Measures
The sensitivity, specificity, positive predictive value (PPV), and
negative predictive value (NPV) of SDA for the detection of N. gonorrhoeae
compared to culture, and the reproducibility of the assay by repeat
analysis of a subset of samples were determined.
Main Results
N. gonorrhoeae was detected in 130 specimens by culture and 152 by
SDA. Twenty-four of 3,544 samples gave discordant results (table). The
sensitivity, specificity, PPV, and NPV for the SDA system were 99.2%,
99.3%, 84.9%, and 99.9%, respectively. Upon retesting, 135 of 152 SDA
positive samples remained positive, and 272 of 280 SDA negative samples
remained negative. Of the 23 samples that were SDA positive and culture
negative, only 7 were positive on repeat analysis. Fifty percent of these
23 samples had SDA assay signals close to the cut-off value.
| Observed initial
results of BDProbeTec-SDA system compared to culture in 3544 urine
specimens |
| SDA
Results |
Culture
Results |
| positive |
negative |
total |
| positive |
129 |
23 |
152 |
| negative |
1 |
3391 |
3392 |
| total |
130 |
3414 |
3544 |
Authors' Conclusions
The BD ProbeTec-SDA assay is a sensitive and
specific method for the detection of N. gonorrhoeae in urine
samples from men and women. Culture confirmation is needed for samples
with positive results from populations in which the N. gonorrhoeae
prevalence is low.
Source of funding: None given.
For correspondence: Franklyn Judson,
Denver Public Health, 605 Bannock St., Denver, CO 80204-4507. E-mail
address: frank.judson@dhha.org.
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