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Self collected
specimens offer women in remote communities an acceptable and
sensitive alternative method of testing for STIs.
Evaluation of
self-collected samples in contrast to practitioner-collected samples for
detection of Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas
vaginalis by polymerase chain reaction among women living in remote
areas.
Knox J, Tabrizi SN, Miller P, Petoumenos K,
Law M, Chen S, Garland SM.
Sex Trans Dis. 2002;29:647-654.
Summary:
Question
How do self-collected sampling methods compare to conventional
practitioner-collected endocervical samples for the PCR detection of C.
trachomatis and N. gonorrhoeae, and how do two self-collected
sampling methods compare for the PCR detection of T. vaginalis?
Design
The results of PCR on urine, vaginal swab, and tampon samples collected by
women in urban and remote areas were compared to those of endocervical
swabs collected by practitioners during a clinical examination for the
detection of N. gonorrhoeae and C. trachomatis; and the
results of PCR on vaginal swab and tampon samples were compared for the
detection of T. vaginalis.
Participants
Two hundred sixty-two Aboriginal and 56 non-Aboriginal women from urban (n
= 74) and remote (n = 244) areas of central Australia attending
their health clinic for a check-up that required a pelvic examination were
tested.
Description of Tests and Diagnostic
Standard
Six specimens were collected from each participant. Before examination,
each woman collected 10 to 20 ml of urine, a low vaginal swab that was
placed in a dry tube, and a tampon, which was inserted, immediately
removed, and placed into transport medium. During a speculum examination,
the practitioner collected a high vaginal swab that was placed into
transport medium, an endocervical swab that was rolled onto a glass slide
and then placed into transport medium, and a second endocervical swab that
was placed in a dry tube. The high vaginal swab was used for wet mount and
T. vaginalis culture in trichomonas broth (Oxoid, Hampshire, UK).
The endocervical slide was Gram stained and the swab in transport medium
was used for N. gonorrhoeae culture. Identification of N.
gonorrhoeae was made by performing an oxidase test, monoclonal
antibody test (Boule Diagnostics, Sweden), and Gonocheck-II (EY
Laboratories, San Mateo, CA).
The urine, self-collected vaginal swab,
and endocervical swab in the dry tube were processed and tested for C.
trachomatis, N. gonorrhoeae and an internal control according to the
protocol for the COBAS Amplicor assay (Roche Diagnostics, Branchburg, NJ).
DNA was extracted from the tampon cell pellet and tested by COBAS.
Internal control-negative results were confirmed by repeated testing. When
only one sample from a participant was positive for C. trachomatis,
a confirmatory test was performed with a second PCR with primers directed
to a major OMP. Participants were considered positive for C.
trachomatis if positive results were obtained from at least two
samples or with confirmation by OMP-PCR when only one sample was positive.
All PCR-positive N. gonorrhoeae specimens were confirmed with a 16S rRNA
PCR assay (Roche). Participants were considered positive for N.
gonorrhoeae if any one sample was confirmed positive by 16S rRNA PCR.
DNA extracted from the tampon cell pellet
and an aliquot of the vaginal swab were tested using a noncommercial PCR
assay for T. vaginalis that used primers TVA5-TVA6. A second PCR
for amplification of ?-globin DNA using primers PC04-GH20 was included as
a positive control. PCR products were hybridized by probes TB and PC03 for
T. vaginalis and ?-globin, respectively, and detected by Enzymum-Test
DNA Detection Assay (Boehringer Mannheim). When T. vaginalis was
detected in only one specimen by PCR, samples were tested by amplification
with a second primer pair that amplified the repeated DNA fragment.
Participants were considered positive for T. vaginalis if a
positive result occurred by any of the following methods: wet preparation,
culture, PCR positive for both swab and tampon, and PCR positive for
either swab or tampon and confirmed by the second PCR
Main Outcome Measures
Sensitivity, specificity, positive predictive value (PPV), and negative
predictive value (NPV) for each specimen type tested were compared to the
final result per participant, as obtained after confirmation as defined
above. Observations from a participant were included if at least two
specimens were assessable, as determined by a positive test for the
internal controls.
Main Results
The overall prevalence of STIs among the participants was 11.5% for C.
trachomatis, 11.8% for N. gonorrhoeae, and 24.6% for T.
vaginalis. The sensitivity, specificity, PPV, and NPV of PCR for the
detection of C. trachomatis, N. gonorrhoeae, and T. vaginalis
in each specimen type are shown in the table. Detection of C. trachomatis
and N. gonorrhoeae was most sensitive with tampon specimens and
least sensitive with urine. Sensitivity of microscopy and culture versus
PCR for detection of T. vaginalis and N. gonorrhoeae was
52.4% and 53.6%, respectively. No samples positive by culture were
negative by PCR.
| Performance of PCR
assays for detection of STIs by specimen type |
| Test
specimen |
Organism |
PCR
performance parameter, % (95% CI) |
| Sensitivity |
Specificity |
PPV |
NPV |
| Tampon |
C.
trachomatis |
100
(89.7-100) |
99.3
(85.4-99.8) |
94.4
(81.3-99.3) |
100
(98.6-100) |
| N.
gonorrhoeae |
97.2
(85.5-99.9) |
100
(98.6-100) |
100
(90.0-100) |
99.6
(97.9-99.9) |
| T.
vaginalis |
100
(93.7-100) |
100
(97.9-100) |
100
(93.7-100) |
100
(97.9-100) |
| Self-collected
vaginal swab |
C.
trachomatis |
84.8
(69.1-93.4) |
99.6
(97.7-99.9) |
96.6
(82.2-99.9) |
98.0
(95.3-99.1) |
| N.
gonorrhoeae |
71.9
(53.3-86.3) |
100
(98.5-100) |
100
(85.2-100) |
96.4
(93.4-98.1) |
| T.
vaginalis |
87.7
(76.8-93.9) |
100
(97.9-100) |
100
(92.9-100) |
96.2
(92.3-98.1) |
| Endocervical
swab |
C.
trachomatis |
92.3
(75.9-97.9) |
99.5
(97.5-99.9) |
96.0
(79.7-99.9) |
99.1
(96.8-99.8) |
| N.
gonorrhoeae |
92.6
(75.7-99.1) |
100
(98.3-100) |
100
(86.3-100) |
99.1
(96.8-99.8) |
| Urine |
C.
trachomatis |
72.7
(55.8-84.9) |
100
(98.9-100) |
100
(85.8-100) |
96.4
(93.2-98.1) |
| N.
gonorrhoeae |
31.2
(16.1-50.0) |
100
(98.5-100) |
100
(69.2-100) |
91.6
(87.6-94.3) |
Authors' Conclusions
Tampons and self-collected swabs provide
women with an alternative way of testing for STI that is both acceptable
and sensitive.
Source of funding: Royal Women's
Hospital, Departments of Microbiology and Infectious Diseases, Melbourne;
Western Diagnostic Pathology; Roche Diagnostics; Tristate STD/HIV Project;
National Center in HIV Epidemiology and Clinical Research.
For correspondence: Sepehr Tabrizi,
132 Grattan Street, Carlton, Victoria 3053, Australia. E-mail address:
tabrizis@cryptic.rch.unimelb.edu.au.
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