Directly detecting Chlamydia trachomatis using PCR

Pathogen
Chlamydia trachomatis, serotypes D-K, is one of the world’s most prevalent pathogens that cause sexually transmitted diseases. Newborns can become infected with it in the birth canal. Serotypes A-C, which cause trachoma, and L1-L3, which cause Lymphogranuloma venerum, are rare in Germany.

Symptoms
In men, urethritis, epididymitis, prostatitis and proctitis are all typical manifestations of an acute Chlamydia trachomatis infection. In women, symptoms include urethritis, Bartholinitis, cervicitis, salpingitis, endometritis and pelvic inflammatory disease (PID). Up to 80 % of these infections are initially asymptomatic. The consequences of a chronic infection include infertility, ectopic pregnancy and premature births.
Transmission of the pathogen during birth can cause, among other things, conjunctivitis and neonatal pneumonia.
Since 2008, screening for asymptomatic Chlamydia infections in pregnant women (during maternity care), and once a year in young women up to the age of 25 years (in the context of the „Guidelines for Birth Control and Abortion”) by nucleic acid amplification techniques (NAT) has been a service provided by statutory health insurance.

Laboratory
The direct detection of pathogens using NAT has largely replaced antigen detection (ELISA or immunofluorescence), while cytology and culture-based testing are procedures reserved for specific clinical issues. In addition, the indirect detection of pathogens by detecting antibodies (IgA and IgG) in the serum is an available option that is especially valuable for differential diagnostics in chronic infections and for epidemiological questions.
A specificity of nearly 100 % with a sensitivity of over 95 % is reported for qualitative direct detection of Chlamydia DNA using a polymerase chain reaction (PCR) that detects all serotypes of Chlamydia trachomatis. Therefore, along with diagnosing symptomatic forms, it is also suitable for screening for asymptomatic infections.

Material and preanalytics
In men, the pathogen density is about the same in first-void urine as in urethral smears; in women, it is lower by a factor of around 10 in urine compared to cervical and vaginal smears.
This means that, in men, urethral swabs and first-void urine are more or less equally well suited for diagnostic purposes. A prostate discharge and ejaculate can also be tested when there is a question of prostatitis and epididymitis (Abbott multi-Collect).
In women, examination materials that are particularly well suited are endocervical and vaginal smears; for Chlamydia screening, however, urine has been established as the test material. To ensure the maximum level of sensitivity, we recommend sending in first-void urine samples for this. In these cases, please enter „Chlamydia screening” on the transfer form and tick the „preventive” field.
For all test materials, please use the special sampling utensils, which you can request from the laboratory.

Notes on taking smears
Smears (vaginal, endocervical or urethral):
Before taking urethral smears, the patient should not have passed water for at least one hour previously.

  • Remove the sterile swab from the protective foil.
  • Introduce the white tip of the swab into the sampling site.
  • Rotate the swab slightly (endocervical and vaginal swabs 15-30 sec, urethral swabs 2-3 sec).
  • Carefully pull out the swab.
  • Handle the cap and the tube with care to avoid contamination.
  • Open the cap of the transport tube and insert the swab immediately into the transport tube with the white tip pointing down.
  • Carefully break off the swab at the break-away edge of the grip.
  • Seal and label the sample.

First-void urine:
The patient should not have passed water for at least one hour prior to giving the sample.
The first 20 to 30 ml of urine should be collected in a urine beaker.

  • Carefully open the cap of the transport tube and discard the swab.
  • Handle the cap and the tube with care to avoid contamination.
  • Transfer the urine with the plastic transfer pipette into the sample tube until the filling level reaches the filling level window shown on the tube’s label.
  • Do not overfill!
  • Seal and label the sample.
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