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Dry transported
intravaginal swabs were as accurate as wet swabs for detection of C.
trachomatis and N. gonorrhoeae by PCR.
Evaluation of dry and
wet transported intravaginal swabs in detection of Chlamydia
trachomatis and Neisseria gonorrhoeae infections in female
soldiers by PCR.
Gaydos CA, Crotchfelt KA, Shah N, Tennant M, Quinn TC, Gaydos JC, McKee
KT, Rompalo AM.
Journal of Clinical Microbiology 2002;40:758-761.
Summary:
Question
Are intravaginal swabs transported by mail in a dry state as accurate as
wet swabs for PCR detection of chlamydia and gonorrhea?
Design
This paper describes a cross-sectional study of chlamydia and gonorrhea
infections of active-duty military women attending an STD clinic in which
PCR tests of vaginal swabs transported in wet and dry states were compared
to conventional testing methods.
Participants
Seven hundred ninety-three consecutive active-duty military women, 18 to
59 years of age, attending a military clinic and presenting for evaluation
of genitourinary symptoms (83%), for therapy as a known contact of an
individual with a diagnosed STD, or for routine STD screening were
studied. Sixty percent of participants were African-American, 33% were
Caucasian, the remainder were of other racial backgrounds.
Description of Tests and Diagnostic
Standard
Intravaginal swabs were collected for the following tests: 1) a swab
placed in transport medium for PCR (Amplicor CT/NG, Roche Molecular
Systems, Branchburg, NJ) wet testing, 2) a swab placed in a sterile tube
with no fluid for PCR, and 3) a swab placed in transport buffer for ligase
chain reaction (LCR, Abbott Laboratories, Abbott Park, IL). Cervical swabs
were obtained for: 1) chlamydia EIA (Syva Company, San Jose, CA), 2)
gonorrhea culture (modified Thayer-Martin medium), and 3) discrepant
chlamydia (Roche OMP-1 gene) and gonorrhea (Roche DNA methlytransferase
gene and the 16S rRNA gene) PCR analysis, as necessary. Samples were
maintained and shipped at 4oC. Swabs were processed according to the
manufacturers' instructions for each assay. For the dry swabs, transport
buffer was added to the tube after receipt in the laboratory and before
processing. True chlamydia positives among samples with discrepant EIA and
CT/NG PCR results were defined as samples for which either the original
positive PCR or positive EIA was confirmed by another C. trachomatis
DNA amplification test (LCR or OMP-1 PCR). True gonorrhea positive samples
among discrepant samples negative by culture and positive by CT/NG PCR
were defined as samples that were positive by two DNA amplification tests
for two different N. gonorrhoeae genes.
Main Outcome Measures
The sensitivities and specificities for the detection of C. trachomatis
and N. gonorrhoeae using vaginally obtained swabs tested by PCR
(wet and dry transport method) and cervical swabs tested by EIA
(chlamydia) and culture (gonorrhea) were calculated using the adjudicated
true-positive and true-negative results as described above.
Main Results
The performances of the Amplicor CT/NG PCR assay performed on wet and dry
transported vaginal swabs and of EIA for chlamydia and culture for
gonorrhea performed on cervical swabs for the detection of C.
trachomatis and/or N. gonorrhoeae are shown in Table 1. After
resolving discrepant samples by additional testing of vaginal and cervical
swabs with other amplification assays, 92 and 27 samples were defined as
true-chlamydia and gonorrhea positives, respectively. The sensitivity and
specificity of each assay by organism, after adjudication of discrepant
results, are shown in Table 2.
| Table 1. Performance
of PCR of wet and dry transported vaginal swabs, and EIA and culture
of cervical swabs for the detection of C. trachomatis and
N. gonorrhoeae |
| Test |
C.
trachomatis |
N.
gonorrhoeae |
|
Positive |
Negative |
Positive |
Negative |
| Wet swab
PCR |
92 |
701 |
40 |
753 |
| Dry swab
PCR |
85 |
708 |
39 |
754 |
| EIA |
74 |
719 |
|
|
| Culture |
|
|
17 |
776 |
Table 2. Performance of PCR of wet
and dry transported vaginal swabs, and EIA and culture of cervical
swabs for the detection of C. trachomatis and N.
gonorrhoeae after adjudication of discrepant samples |
| Test |
C.
trachomatis |
N.
gonorrhoeae |
|
Sensitivity (%) |
Specificity
(%) |
Sensitivity
(%) |
Specificity
(%) |
| Wet swab
PCR |
94.6 |
99.3 |
96.3 |
98.2 |
| Dry swab
PCR |
91.3 |
99.3 |
88.9 |
98.3 |
| EIA |
72.9 |
99.0 |
|
|
| Culture |
|
|
63.0 |
100 |
Authors' Conclusions
A vaginal swab that was transported to the
laboratory in a dry state was as accurate as a wet swab shipped in the
liquid transport medium recommended by the manufacturer for the detection
of C. trachomatis and N. gonorrhoeae by PCR amplification.
Source of funding: Department of the
Army
For correspondence: Charlotte Gaydos,
Johns Hopkins University School of Medicine, 1159 Ross, 720 Rutland Ave.,
Baltimore, MD 21205. E-mail address: cgaydos@jhmi.edu.
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