Definitions for the level of evidence (I-IV) and grade of recommendation (A-C) are provided at the end of the "Major Recommendations" field.
Available Tests
Nucleic Acid Amplification Tests (NAATs)
The role of the nucleic acid amplification technology in the routine diagnosis of Chlamydia Trachomatis (C. trachomatis) infections is evolving rapidly. Three commercial assays are now available for routine use:
- Polymerase chain reaction (PCR; Roche Diagnostics)
- Strand displacement amplification (SDA; Becton Dickinson)
- Transcription mediated amplification (TMA; GenProbe)
Although these commercial assays differ in their target sequence and their method of amplification, it is their ability to produce a positive signal from theoretically a single copy of the target DNA or RNA (see pack inserts from the kit manufacturers) that has lead to the reported increased sensitivity of NAATs. Similar to other nonculture tests, NAATs do not require viable organisms.
With the advent of molecular diagnostic technology, it is now appreciated that no single test provides 100% sensitivity and specificity. Currently, NAATs are proving to be the best tests on the market. There is no room for complacency, however, as further work is required to eliminate test problems, such as inhibitors, contamination, reproducibility, and hormonal factors, that have played a part in lowering sensitivity.
Confirming Positive NAATs by Another Technique
Only another NAAT is sensitive enough to confirm a positive result. This approach needs further evaluation, as it is rare that individual laboratories will be able to offer more than one NAAT platform.
Equivocal Results
Re-test the original sample (according to manufacturer's instructions).
Inhibition
Inhibitors can be identified from all sites, in particular first-void urine. An internal amplification control to identify inhibition should be used and is available using some of the commercial kits. The Gen-Probe TMA test has a stage in the extraction process which the manufacturer claims removes the majority of inhibitors and therefore no inhibitory control is needed (see individual manufacturer's instructions).
Pooling Samples
This is possible and improves cost efficiency but is not licensed. Optimal pool sizes will vary according to the prevalence in the population being tested.
Tissue Culture (TC)
The traditional method of diagnosing C. trachomatis was by cell culture. However, few laboratories in the United Kingdom (UK) still offer this service. Cell culture procedures are expensive, labour intensive and time consuming.
Although chlamydiae are bacteria, they cannot be cultivated in non-living or cell free media. Tissue culture techniques vary among laboratories. With no standardised protocol it is difficult to compare interlaboratory performance. Cell culture detects only viable organisms, and hence, as with any other bacterial investigation the specimen collection and transport to the laboratory has to be optimal, irrespective of which laboratory method is to be used. Even under ideal conditions the sensitivity is probably no more than 75%, although specificity should be 100% if a C. trachomatis- major outer membrane protein (MOMP)-specific stain is used.
Direct Fluorescent Antibody (DFA)
Specimen material is obtained with a swab or brush, which is then rolled over the specimen well of a slide. Once air dried and fixed the specimen can be stained using either a MOMP or lipopolysaccharide (LPS) fluorescein-labelled monoclonal antibody that binds to C. trachomatis elementary bodies. Stained elementary bodies can then be identified using a fluorescence microscope. This technique is ideally suited for small numbers. It can give a quick turnaround time, but its sensitivity and specificity are dependent on the expertise of the laboratory. DFA detects both viable and non-viable organisms.
This is the only test allowing simultaneous assessment of specimen adequacy.
Enzyme Immuno Assay (EIA)
There are many commercially available EIA tests on the market for detecting C. trachomatis infection. They detect chlamydial LPS with a monoclonal or polyclonal antibody that has been labelled with an enzyme. The enzyme converts a colourless substrate into a coloured product, which is detected by a spectrophotometer.
As the EIA detects LPS, there is a potential that cross reaction occurs with other microorganisms causing a false positive reaction, hence it is vital that confirmation either by DFA or blocking antibody test is performed.
Sensitivity has been shown to be lower than for NAATs.
"Point of Care"/Serological Tests/Leukocyte Esterase Tests
As they stand at present, these tests are not advised for diagnosis of genital C. trachomatis in the genitourinary medicine (GUM) setting (Grade of Recommendation C).
Recommendations
Because of the superior sensitivity and good specificity of NAATS these are the tests of choice for urethral, cervical and first catch urine specimens (Grade of Recommendation A).
Sites for Testing
Guidance on how to take samples can be made by following the pack inserts from the different manufacturer's kits.
First Catch Urine (FCU) — Grade of Recommendation C
- First 15 to 50 mls of urine passed anytime of the day. Patient must not have urinated for at least one hour (maybe 2 hours for some kits). Follow manufacturer's instructions.
- First catch urine (FCU) is both male and female licensed for most NAATs, although less sensitive than from urethral or endocervical specimens.
- Male urine is licensed for some EIAs, shown to be sensitive with symptomatic, relatively insensitive for asymptomatic males.
- Female urine is unsuitable for EIAs.
- Urine is suitable but not ideal for DFA, needs expertise.
- Urine is unsuitable for tissue culture techniques.
Cervical, (Cx)
Cervical samples are suitable for all tests. Taken under speculum examination, the swab inserted into the os using the manufacturer's swab collection packs and rotated two or more times for 15 to 30 seconds (Grade of Recommendation C).
Urethral, (Ur)
- Both male and female urethral samples are suitable for all tests.
- For men the swab is inserted into the urethra 2 to 4 cm and rotated one or more times (Grade of Recommendation C).
Pharynx, (Ph)
- Pharyngeal samples licensed for tissue culture technique (Grade of Recommendation A).
- DFA is licensed for pharyngeal swab specimens but not suitable for large throughput use (Grade of Recommendation C).
- Not licensed for most EIAs.
- NAAT not licensed but increasing work on validation means that for any centre without access to culture this is the test of choice (Grade of Recommendation C).
Rectal, (Re) (obtained via proctoscopy)
- Rectal samples validated for tissue culture technique (Grade of Recommendation A).
- DFA is licensed for rectal swab specimens but not suitable for large throughput use (Grade of Recommendation C).
- Not licensed for EIA testing owing to the cross reaction with other organisms leading to false positive EIA results.
- Routinely available NAATs for C. trachomatis will detect all serovars including lymphogranuloma venereum (LGV) serovars and are licensed for genital specimens. There are no licensed NAATs for the detection of C. trachomatis in rectal specimens but data is available supporting the validity of these tests for use with rectal specimens and therefore for centres without access to culture this is the test of choice (Level of Evidence III, Grade of recommendation B).
Vulval-Vaginal, (VV)
Not licensed for use with NAATs, but demonstrated by a number of workers to produce equivalent sensitivity to cervical testing.
Table 1: Summary of Recommended Tests for Use with Different Sites of Samples
| |
Sites |
| Test |
FCU |
Cx |
Ur |
Ph |
Re |
VV |
| NAAT |
1 |
1 |
1 |
3 |
3 |
3 |
| ELISA |
4 |
2 |
2 |
5 |
5 |
5 |
| DFA |
2 |
2 |
2 |
2 |
2 |
5 |
| TC |
5 |
2 |
2 |
1 |
1 |
5 |
FCU, first catch urine; Cx, cervix; Ur, urine; Ph, pharynx; Re, rectal; VV, vulval/vaginal; NAAT, Nucleic Acid Amplification Tests; ELISA, enzyme-linked immunosorbant assay; DFA, direct fluorescent antibody; TC, tissue culture
Key
- Test of choice
- Acceptable, but not first choice
- Not licensed, although encouraging work being performed
- Only for use in asymptomatic males
- Not recommended
All recommendations are at level B unless stated otherwise.
Screening in the Following Patient Groups
Owing to the frequently asymptomatic nature of genital C. trachomatis there is no difference in the screening guidelines for those showing symptoms to those who do not.
Frequency of Repeat Testing in an Asymptomatic Patient
This is in part being addressed by the Department of Health (DoH) Chlamydia Screening Programme. Re-exposure to a possible source of chlamydia should lead to re-screening if the patient re-presents.
Heterosexual Women
Cervical or vulval-vaginal (clinician or self taken) or first catch urine (Grade of Recommendation A)
Heterosexual Men
Urethral or first catch urine (Grade of Recommendation A)
Homosexual Men
Urethral or first catch urine (Grade of Recommendation A)
Young Women
- Offer non-invasive tests if speculum examination is declined
- Vulval-vaginal (clinician or self-taken) or first catch urine (Grade of Recommendation A)
Young Men
- Offer non-invasive testing if urethral specimen is declined
- First catch urine (Grade of Recommendation A)
Pregnant Women
As for heterosexual women. See notes below on test of cure (TOC).
Contacts
No different advice
Sex Workers
No different advice
Sexual Assault Victims
Culture was the recommended method for detecting C. trachomatis at all exposed sites following sexual assault in adults because of 100% specificity (Grade of Recommendation C). This guideline recommends that a NAAT be taken from all exposed sites in addition to a chlamydial culture (if culture is available) owing to the low sensitivity of culture and lack of availability.
Test of Cure (TOC)
Test of cure is not routinely recommended if standard treatment has been given, there is confirmation that the patient has adhered to therapy and there is no risk of re-infection. However, if these criteria cannot be met or if the patient is pregnant a TOC is advised. This should be taken using the same technique as used for the initial testing. Ideally, a minimum of 3 to 5 weeks post treatment is required as NAATs will demonstrate residual DNA/RNA even after successful treatment of the organism (Grade of Recommendation A).
Definitions:
Levels of Evidence
Ia: Evidence obtained from meta-analysis of randomised controlled trials
Ib: Evidence obtained from at least one randomised controlled trial
IIa: Evidence obtained from at least one well designed controlled study without randomisation
IIb: Evidence obtained from at least one other type of well designed quasi-experimental study
III: Evidence obtained from well designed non-experimental descriptive studies
IV: Evidence obtained from expert committee reports or opinions and/or clinical experience of respected authorities
Grading of Recommendations
- Evidence at level Ia or Ib
- Evidence at level IIa, IIb, or III
- Evidence at level IV
