|
The sensitivity of
a PCR assay exceeded that of wet prep and culture for the detection
of T. vaginalis in women attending an STD clinic.
Trichomonas vaginalis polymerase
chain reaction compared with standard diagnostic and therapeutic
protocols for detection and treatment of vaginal trichomoniasis.
Wendel KA, Erbelding EJ, Gaydos CA,
Rompalo, AM.
Clin Infect
Dis. 2002;35:576-580.
Summary:
Question
What is the reliability of a PCR assay compared to wet preparation and
culture for the detection of T. vaginalis, and how does the number
of patients with T. vaginalis infection who receive metronidazole
treatment under current clinical algorithms compare with the projected
number who would receive treatment if PCR were used for diagnosis?
Design
This study describes a cross-sectional, retrospective comparison of the
results of a T. vaginalis PCR assay with those of wet preparation,
Papanicolaou smear, and culture for detection of T. vaginalis
infection in high-risk women. The number of women who received treatment
using CDC guidelines was compared to the number who would have received
treatment if PCR had been used for diagnosis.
Participants
Three hundred thirty-seven women attending a Baltimore City Health
Department STD clinic who had not received antibiotic therapy within the 2
weeks prior to their visit were tested. Ninety-eight percent were
African-American, and the mean age was 28 years. Seventy percent were
symptomatic, and 21% had recent exposure to a partner with an STD.
Description of Tests and Diagnostic
Standard
Swab specimens from the posterior fornix of the vagina were mixed with 2-3
drops of normal saline on a slide and examined microscopically for
evidence of motile T. vaginalis. A second swab specimen was used to
inoculate an InPouch TV test (Biomed Diagnostics), which was incubated at
37oC and examined microscopically at 1, 2, and 5 days. Cervical samples
were obtained with an Ayre spatula, fixed on a slide, and Papanicolaou
stained. Vaginal swabs stored frozen in PCR buffer (Amplicor, Roche
Diagnostics) were thawed and 100 µL was processed with Amplicor specimen
buffers. The PCR primer set BTUB 9/2 was used to target 112-bp conserved
regions of the 3 b-tubulin genes of T. vaginalis. Amplicons were
electrophoresed on agarose gels, stained with ethidium bromide, and
compared with commercial size markers. Discordant results between BTUB 9/2
PCR and cultures were adjudicated with primer sets TVK 3/7 and AP65 A/B.
True positive samples were defined as those positive for T. vaginalis
by wet prep, culture, or by PCR that was confirmed with a second primer
set.
Main Outcome Measures
The sensitivity and specificity of each of the diagnostics methods for
true T. vaginalis infection as defined above were determined.
Main Results
T. vaginalis infection was detected in 97 (29%) of 337 women. The
performance characteristics of the T. vaginalis diagnostic assays
are shown in the table. Metronidazole treatment was provided to 67 (69%)
of 97 positive women based on current clinical algorithms. The use of the
PCR assay for diagnosis of trichomoniasis would have allowed treatment of
81 (84%) of 97 women with T. vaginalis infection.
| Performance
characteristics of T. vaginalis diagnostic assays performed
on 337 women. |
| Assay |
%
Sensitivity
(95% CI) |
%
Specificity
(95% CI) |
| Wet
preparation |
52
(41-62) |
100 |
| Papanicolaou
smear |
24
(15-34) |
99
(97-99.9) |
| Culture |
78
(69-86) |
100 |
| PCR |
84
(75-90) |
94
(90-97) |
Authors' Conclusions
The sensitivity of PCR for the detection of T.
vaginalis exceeded that of wet preparation and culture, and its
specificity was high. Use of T. vaginalis PCR would improve the
identification and treatment of T. vaginalis infections.
Source of funding: Not given.
For correspondence: Karen Wendel, 921
NE 13th St. (111C), Oklahoma City, OK 73104. E-mail address: karen-wendel@ouhsc.edu.
|
.gif){kind=small}