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A ligase chain
reaction amplification assay performed on urine specimens was more
sensitive than an enzyme immunoassay on cervical and urethral swabs
for the detection of C. trachomatis.
Screening for genital chlamydia
infection: DNA amplification techniques should be the test of choice.
Harindra V, Underhill G, Tobin JM.
International
Journal of STD & AIDS 2003;14:723-726.
Summary:
Question
How do the results of a ligase chain reaction amplification assay
performed on urine samples compare to those of an enzyme immunoassay
performed on pooled endocervical and urethral swabs from women and
urethral swabs from men for the detection of C. trachomatis?
Design
The results of a C. trachomatis ligase chain reaction (LCR) DNA
amplification assay performed on first void urine specimens were compared
to the results of a C. trachomatis enzyme immunoassay (EIA)
performed on pooled endocervical/endourethral swabs from women and on
endourethral swabs from men.
Participants
Men (n=1247) and women (n=1835) taking part in the UK chlamydia screening
pilot, a prospective screening of women attending primary health care
settings (11% GUM, 60% general practice, 26% family planning, and 3%
other) and men attending GUM or SexSense in Portsmouth, UK, were tested.
Participants were between 16 to 24 years old. However, those under 16
years old who attended for sexual health issues were also included.
Description of Tests and Diagnostic
Standard
A first void urine specimen for analysis by C. trachomatis LCR
(Abbott Laboratories, Maidenhead, UK) was collected from every subject as
part of the screening pilot. The assay was carried out according to the
manufacturer's protocol except that the range for equivocal results was
set at 0.5 to 1.5. The assay was repeated on samples with positive and
with equivocal results. Pooled urethral and cervical swabs from women and
urethral swabs from men were tested for C. trachomatis by EIA (Microtrak
II, Trinity Biotech, Ireland). Men and women attending GUM clinics had
swabs taken before providing a urine specimen. Patients seen in other
settings had their swabs collected approximately two weeks after providing
the urine sample. All EIA positive samples were confirmed using
immunofluorescence (Microtrak). Only patients who had non-equivocal
results on both tests were included in the analyses.
Main Outcome Measures
The results of the LCR and the EIA for the detection of C. trachomatis
in samples from men and women were compared.
Main Results
The number of specimens from women and men who had positive results with
either or both tests are shown in the table. In women, EIA on pooled swabs
detected 575 of the 785 specimens positive by either or both assays. In
men, EIA detected 209 of 351 positive specimens. The sensitivity of EIA
for the detection of C. trachomatis by either assay was 73% and 60%
in women and men, respectively. The sensitivity of LCR was 98% for samples
from both men and women. The results were similar for patients seen at the
GUM and at other clinical settings.
Authors' Conclusions
The sensitivity of the EIA was low compared
to the LCR when used to analyze specimens from a large population-based
screening study. Twenty-seven per cent of women and 40% of men with
chlamydia infection, as determined by the result of either assay, had a
false negative EIA result. The discrepancy between LCR and EIA was greater
with male specimens.
Source of funding:
The Chlamydia Pilot Study was funded by the Department of Health (UK)
For correspondence:
V. Harindra, Department of Genito-Urinary Medicine, St. Mary's Hospital,
Milton Road, Portsmouth PO3 6AD, UK. E-mail address: veerakathy.harindra@porthosp.nhs.uk
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