DNA methods should be used to detect Chlamydia trachomatis
BMJ 1998; 317 doi: https://doi.org/10.1136/bmj.317.7171.1525 (Published 28 November 1998) Cite this as: BMJ 1998;317:1525
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EDITOR-
The recent letter from Taylor-Robinson and Robinson (1.) regarding
the use of DNA amplification methods for the diagnosis of chlamydial
infections raises several difficult issues. The cost of changing to such
methods is substantial. Our estimate is that it would require an
additional £5.0M p.a. for the current GUM workload. In addition, there are
substantial ‘one off' costs for training, additional space and gaining
formal accreditation before DNA methods can be widely applied. It is clear
from one recent paper (2.) that many laboratories are finding it hard to
come to terms with the high costs of amplification tests, even in affluent
California.
Any expenditure of this magnitude must be based on the best evidence.
A recent, French, multi-centre survey of 28 commercial kits for C.
trachomatis diagnosis (3.) using a dilution series of in vitro grown
Chlamydia found that enzyme-linked immunoassay (EIA) detection limits
varied over a ten-fold range, with only two manufacturers kits attaining
the same values as direct immunofluorescence assays. A previous Bristol
study also found variation in performance using clinical specimens (4.).
Clearly, it is necessary to use the most sensitive EIAs in ‘head to head'
comparative trials to establish the true difference in sensitivities.
There are reports in the literature in which the difference in sensitivity
observed has been much less than that quoted by the authors when the most
sensitive EIAs are used. A recent example is the paper by Tanaka et al.
(5.) on detection in vaginal and cervical swabs where, in both cases, the
best EIA gave sensitivities close to those of PCR.
We are saddened by the suggestion that women who have had a diagnosis
by EIA will recourse to litigation and are unconvinced, given all the
imponderables of chlamydial infection, that they would have any chance of
success. No current test has 100% sensitivity. Would a woman who had a
diagnosis by nucleic acid amplification assay be in a position to sue if
the laboratory had not checked her specimen for inhibitors?
While we understand the authors desire to offer patients the best
test, our concern is that the very high costs of amplification assays will
lead to restrictions on testing. This would be disastrous at a time when
we could be widening chlamydial screening to reach the substantial number
of infected women who currently receive no service at all.
Alan Herring,
Head, PHLS Genitourinary Infections Reference Laboratory,
Bristol PHL,
Myrtle Rd,
Bristol BS2 8EL,
Owen Caul,
Consultant Virologist,
Bristol PHL,
Myrtle Rd,
Bristol BS2 8EL
Ian Paul,
Medical Laboratory Scientific Officer,
Bristol PHL,
Myrtle Rd,
Bristol BS2 8EL
Patrick Horner,
Consultant Physician,
The Milne Centre,
Bristol Royal Infirmary,
Bristol BS2 8HW
1 Taylor-Robinson, D and Robinson, A.J. DNA methods should be used
to detect Chlamydia trachomatis. BMJ 1998;317:1525
2 Dean, D., Ferrero, D., and McCarthy, M. Comparison of performance and
cost-effectiveness of direct fluorescent-antibody, ligase chain reaction,
and PCR assays for verification of chlamydial enzyme immunoassay results
for populations with a low to moderate prevalence of Chlamydia trachomatis
infection. J. Clin .Microbiol 1998. 36(1):94-99.
3 Biachi, A., De Barbeyrac, B., Bebear, C., Buffet-Janvresse, C. Eb, F. ,
Janot, C. Maisonneuve, P., Migueres, M., Orfila, J., Scieux, C. and
Alonso, J. Multi-laboratory comparison of 28 commercially available
Chlamydia trachomatis diagnostic tests.In ‘Chlamydial Infections' Edited
by R.S.Stephens et al. 1998. ISBN 0-9664383-0-2.
4. Paul, I.D. and Caul, E.O. Evaluation of three Chlamydia trachomatis
immunoassays with an unbiased, non-invasive clinical sample.
J.Clin.Microbiol. 1990; 28;220-222.
5. Tanaka, M., Nakayama, H., Yoshida, H., Takahashi, K., Nagafuji, T.,
Hagiwara, T. and Kumazawa, J.
Detection of Chlamydia trachomatis in vaginal specimens from female
commercial sex workers using a new improved immunoasay. Sex. Transm. Inf.
1998. 74:435-438.
Competing interests: No competing interests
Testing for chlamydia
Sir,
In the BMJ of 16 May 1998, the launch of a pilot screening programme for
Chlamydia trachomatis infection was reported (1). The screening test to
be used can be performed on urine specimens, making it a non-invasive
test, and therefore more acceptable to patients. In the same edition, an
editorial acknowledges the importance of acceptability of a test for
chlamydia (2), impliciily accepting that the currently used tests, all of
which require invasive sampling, may not be the best ones with which to
promote such a programme. We believe this is true not only of screening,
but of diagnostic tests in Genitourinary Medicine clinics (GUM) and
describe a case in which non-invasive testing would have been a great
advantage.
A fifteen year old girl attended GUM with a two day history of vulval
soreness and itching associated with increased vaginal discharge. She
reported having being raped five days previously by an unknown assailant
and had a regular sexual partner of three months duration with whom she
had last had sexual intercourse three weeks previously.
She refused any examination or investigation, but as she likened her
problem to a previous episode of ‘thrush’, she was treated empirically
with clotrimazole cream and a clotrimazole 500 mgs. pessary for self-
insertion. When reviewed one week later she reported that her vaginal
discharge and itch were unaltered and still refused examination.
However, she did reluctantly agree to take herself two vaginal swabs for
wet and dry mount examination.
Motile trichomonads were noted on a wet mount examination and she was
treated with Metronidazole 200 mgs. twice daily for seven days. She was
seen by the Health Adviser for partner notification.
On review 13 days later she was asymptomatic. She still declined any
examination and was reluctant to talk about her infection or recent
assault. In this area, it has been noted that 40% of patients found to
have Trichomonas vaginalis have a concurrent infection with Chlamydia
trachomatis (3). As our patient refused any clinical examination, we
were unable to obtain a sample in order to identify a co-existent
chlamydial infection. She was therefore given antichlamydial treatment on
epidemiological grounds to ensure that she did not develop a chronic
chlamydial infection with its complications.
This case demonstrates the problems that some patients have with genital
examination and the value of self-taken swabs and, if possible, urine
specimens for testing. Unfortunately, this Health Board area does not
have facilities for DNA amplification chlamydial testing, necessitating
endocervical and urethral swabs to be taken for chlamydia screening. Not
only does this mean that a significant proportion of chlamydial infections
remain undiagnosed (4), but we do not know how many potential patients are
deterred from attending GUM by the knowledge of the uncomfortable method
of taking specimens; certainly, there are patients who delay coming in
the hope that that whatever they have clears up spontaneously.
One of the Health of the Nation (5) objectives is ‘to reduce the incidence
of sexually transmitted diseases’. The obvious and easiest way to
achieve this is to shut all GUM clinics! However, what we ought to be
looking for, by fulfilling the second objective (‘to provide effective
services for diagnosis and treatment of STDs’) is an increase in numbers
of diagnosed and treated cases. This would reflect better detection and
management, and perhaps a true reduction in the overall prevalence.
As chlamydial infection is the commonest treatable STD in the UK, one of
the most helpful tools in this quest would be the widespread introduction
of DNA amplification techniques into chlamydial diagnostics, so that a
wider population than just that attending GUM could be tested without
being put off by the prospect of the current invasive methods of sampling.
References
(1) Bower H. Britain launches pilot screening programme for chlamydia.
BMJ 1998;316:1479
(2) Boag F, Kelly. Screening for Chlamydia trachomatis. BMJ
1998;316:1474
(3) Thompson C. Genital warts, trichomoniasis and other concurrent STIs
in Scotland. Int J STD&AIDS 1997;8:412
(4) Taylor-Robinson D, Robinson AJ. DNA methods should be used to detect
Chlamydia trachomatis. BMJ 1998;317:1525
(5) Department of Health ‘The Health of the Nation’: HIV/AIDS and Sexual
Health. 1992
M Porter-Boveri, Clinical Assistant in Genitourinary Medicine
C Thompson, Consultant in Genitourinary Medicine
Dept Genitourinary Medicine,
Kirkcaldy Acute Hospitals NHS Trust,
Victoria Hospital,
Kirkcaldy, KY2 5AH
Competing interests: No competing interests