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Review: Diagnostic
assays for C. trachomatis vary by application and
performance.
Microbiological
aspects of the diagnosis of Chlamydia trachomatis.
Ostergaard L.
Best Pract Res Clin Obstet Gynecol. 2002;16:789-99
Question:
What are the applications, advantages, disadvantages, and performances of
the available diagnostic methods for Chlamydia trachomatis?
Data Extraction:
A descriptive comparison of the currently available diagnostic assays for C.
trachomatis including serology, culture, antigen detection, and
nucleic acid amplification is presented. The importance of predictive
values and the association with prevalence are highlighted.
Main Results
The characteristics of the diagnostic methods described in the article are
summarized in the table. Highly sensitive tests must be used when testing
samples from low prevalence populations because the positive predictive
value, which is dependent on sensitivity, decreases with decreasing
prevalence.
| Diagnostic methods
for C. trachomatis. |
| Category |
Technique |
Target |
Performance |
Advantages |
Disadvantages |
| Serology |
Complement
fixation, MIF, EIA |
Antibodies to
LPS, MOMP antigens |
PPV and NPV
low |
|
Cannot
distinguish between past and cur-rent infections |
| Culture |
Tissue
cell culture, infection confirmed by microscopy after staining with
iodine or fluorescent antibody |
Whole
organism |
100%
specific, sensitivity not optimal due to loss of viability during
specimen transport |
|
Time-consuming,
laborious |
| Antigen
detection |
EIA |
LPS |
Dependent on
OD cut-off value, samples in grey zone require confirmation |
Low cost |
Genus
specific, use only cervical or urethral specimens; specificity
de-creased due to cross-reactivity with other organisms |
| DFA |
LPS, MOMP |
Dependent on
number of organisms required for positive |
Low cost |
Requires
fluorescent microscope and skilled personnel |
| Rapid |
|
Not high |
Fast |
Low diagnostic
accuracy |
| DNA
detection |
Probe
hybridization |
rRNA |
|
|
|
| Nucleic
acid amplification |
PCR,
LCR |
Cryptic
plasmid |
Highly
sensitive, plamid and rRNA present in multiple copies, primers
deter-mine specificity; performance dependent on "gold
standard" and specimen site used for comparison |
Detect
non-viable organ-isms; increased sensitivity al-lows use of
non-invasive, patient-collected specimens |
Risk
of contamination, assays detecting crytic plasmid miss plasmid
negative variants |
| MOMP gene |
| PCR |
16S RNA |
| TMA |
rRNA |
Conclusions
The increased sensitivity of nucleic acid
amplification methods, compared to conventional methods, allows samples to
be taken at home by the patient, possibly resulting in the detection of
asymptomatic infections, which would help lower prevalence and the risk of
complications due to C. trachomatis infection.
Source of funding: Danish Centre for
Evaluation and Health Technology Assessment.
For correspondence: Lars Ostergaard,
Department of Infectious Diseases, Skejby Sygehus, Aarhus University
Hospital, DK-8200 Aarhus N, Denmark.
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