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A PCR assay was
significantly more sensitive than culture for the detection of T.
vaginalis in men attending an STD clinic.
Improved detection by
DNA amplification of Trichomonas vaginalis in males.
Schwebke JR, Lawing LF.
Journal of Clinical
Microbiology 2002;40:3681-3683.
Summary:
Question
How does the performance of a PCR amplification assay compare to culture
for the detection of T. vaginalis in urine and urethral swabs from
men?
Design
This study describes a direct comparison of PCR results for urethral and
urine specimens to those of culture techniques for the diagnosis of T.
vaginalis in men attending an STD clinic.
Participants
Three hundred heterosexual men attending a county health department STD
clinic in Birmingham, AL, for STD screening or the treatment of its
symptoms were included. Men were excluded from participation if they had
urinated in the previous hour or had taken antibiotics during the
preceding 14 days.
Description of Tests and Diagnostic
Standard
Two urethral swabs and 20 mL of first void urine were collected for PCR
and for culture. After agitating in 0.5 mL of water, one swab and 10 mL of
urine were centrifuged, DNA was extracted from the pellets, and analyzed
by PCR using primers specific for T. vaginalis (TV 3/7). The
amplified products were electrophoresed on an agarose gel and visualized
by UV light after staining with ethidium bromide. Samples containing a
300-bp fragment were considered positive. T. vaginalis was cultured
by inoculation of the second swab and an aliquot of the urine pellet into
TV InPouch culture medium (BioMed Diagnostics, San Jose, CA) according to
the manufacturer's instructions.
Main Outcome Measures
The sensitivity, specificity, positive predictive value (PPV), and
negative predictive value (NPV) of PCR and culture of urethral swabs and
of urine for the detection of T. vaginalis as determined by the "gold
standard" of the combined results of urethral swab and urine cultures
were calculated.
Main Results
The prevalence of T. vaginalis by culture was 5% (15/300), compared
with a prevalence of 17% (52/300) by PCR. The performance of PCR and
culture, stratified by specimen type, for the diagnosis of T. vaginalis
in men, as determined by combined culture results of both the urethral
swab and urine, is shown in the table. All culture positive specimens were
PCR positive. There was no significant association between urethral
symptoms or inflammation (defined as >5 polymorphonuclear leukocytes
per oil immersion field) and positive PCR or culture.
| Comparison of
diagnostic tests for T. vaginalis in males |
| Method |
Specimen |
Performance,
% (95% CI) |
| Sensitivity |
Specificity |
PPV |
NPV |
| PCR |
Urine |
100
(74.7-100) |
88
(83.2-91.2) |
30 |
100 |
| Urethral swab |
80
(51.4-94.7) |
93
(89.6-95.8) |
38.7 |
98.9 |
| Culture |
Urine |
73
(44.8-91.9) |
100
(98.3-100) |
100 |
98.6 |
| Urethral swab |
53
(27.4-77.7) |
100
(98.3-100) |
100 |
97.6 |
Authors' Conclusions
For men attending an STD clinic, PCR
analysis of urine specimens was far more sensitive than culture for the
detection of T. vaginalis.
Source of funding: In part by an NIH
Sexually Transmitted Disease Cooperative Research Centers grant and an NIH
Sexually Transmitted Diseases Clinical Trials Unit grant
For correspondence: Jane R. Schwebke,
703 19th St. South, Zeigler Research Building #239, Birmingham, AL
35294-0007. E-mail address: Schwebke@uab.edu.
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