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The ligase chain
reaction method detects more cases of pharyngeal N. gonorrhoeae infection
than does culture.
Increased
sensitivity of DNA amplification testing for the detection of
pharyngeal gonorrhea in men who have sex with men.
Page-Shafer K, Graves A, Kent C, Balls JE, Zapitz VM, Klausner
JD.
Clin Infect Dis. 2002;34:173-176.
Summary:
Question
What is the performance of the ligase chain reaction method compared to
culture for the detection of pharyngeal N. gonorrhoeae infection in
samples from men who have sex with men (MSM)?
Design
This study describes a direct comparison of
a commercial ligase chain reaction assay with culture for the detection of
N. gonorrhoeae in pharyngeal swabs.
Participants
Two hundred consecutively evaluated MSM
presenting to a municipal STD clinic in San Francisco, CA, who reported a
history of performing fellatio and no antibiotic use during the 2 weeks
prior to sample collection were tested. The age range of participants was
18 to 61 years. All were asymptomatic for pharyngeal infection.
Description of Tests and Diagnostic
Standard
Two pharyngeal swabs were obtained from the
posterior pharynx of each patient. One swab was used for conventional
culture on modified Thayer-Martin medium; the other was used for LCR
testing (LCx, Abbott Laboratories, Abbott Park, IL). Specimens that were
LCR positive and culture negative for N. gonorrhoeae were further
tested at Abbott Laboratories using an LCR assay with probes for the N.
gonorrhoeae pilin gene. The performance of each test was calculated based
on a gold standard that defined samples positive by culture or, if culture
negative and LCR positive, confirmed positive by pilin LCR as true
positive samples.
Main Outcome Measures
The number of samples positive and negative for N. gonorrhoeae by each
method, and the sensitivity, specificity, positive predictive value (PPV),
and negative predictive value (NPV) of each method as determined by the
gold standard described above were calculated.
Main Results
The results of the LCR assay versus culture
for the detection of N. gonorrhoeae in pharyngeal specimens
obtained from MSM are shown in the table. N. gonorrhoeae was detected in
4.5% of the specimens by culture and in 11% by LCR. Additional testing by
pilin gene LCR of the 14 LCR positive, culture negative specimens
confirmed the presence of N. gonorrhoeae in 10 (71.4%). However, the
culture positive, LCR negative specimen and the culture negative, LCR
negative specimens were not retested by the pilin LCR. After analysis of
these selected discrepant samples by pilin gene LCR, the sensitivity,
specificity, PPV, and NPV of the LCR assay was 94.7%, 97.8%, 81.8%, and
98.9%, respectively. The sensitivity, specificity, PPV, and NPV of culture
was 47.4%, 100%, 100%, and 94.8%, respectively.
| Results
of LCR versus culture |
| Culture
result |
LCR
assay result |
| Positive |
Negative |
Total |
| Positive |
8 |
1 |
9 |
| Negative |
14 |
177 |
191 |
| Total |
22 |
178 |
200 |
Authors' Conclusions
By this discrepancy analysis, the
sensitivity of the LCR for the diagnosis of infection was much higher than
that of culture, but the specificity was lower.
Source of funding: National Institute
of Dental and Craniofacial Research
For correspondence: Kimberly
Page-Shafer, Center for AIDS Prevention Studies, University of California,
San Francisco, 74 New Montgomery, Ste. 600, San Francisco, CA 94105.
E-mail address: shafer@psg.ucsf.edu.
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