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Sample collection

Female genital tract

Cervical swab: The procedures are generally well known, and will be referred to in outline only.

C. trachomatis grows primarily in the living columnar epithelia of the endocervical canal. It does not grow in the keratinised stratified epithelium of the vaginal vestibule. The so-called "high vaginal swab" beloved of gynaecologists is therefore not an appropriate specimen for chlamydial diagnosis.

Any extraneous pus or discharge should first be removed from the endocervix for Gram stain and culture using a conventional swab or gauze. A fine endocervical swab is then introduced into the endocervical canal, rotated gently for 15 to 30 seconds, then removed for laboratory testing. The precise swab and transport material used will depend on the test being performed; the manufacturer's instructions should be followed. A priori, an adequate specimen would be expected to contain endocervical cells. Even with a sensitive nucleic acid amplification-based method like the Abbott LCR, the rate of specimen positivity was much lower if endocervical cells were absent, although there was not a linear relationship between the number of endocervical cells present and the positivity rate. Red blood cells caused little if any inhibition [Loefelhoelz et al., 2001].

There have been concerns that cervicitis may alter the interpretation of gynaecological cytology screening and thereby compromise combined screening for Chlamydia trachomatis cervicitis and squamous intra-epithelial lesions. Liquid-based cytological methods have been shown to limit obscuring factors and permit the detection of infectious agents by DNA amplification techniques such as the Abbott LCx^® LCR. A study of 590 women at high risk for genital chlamydial infection compared a LCR for C. trachomatis using specimens collected in AutoCyte's preservative fluid with the conventional LCR method using cervical swabs. The results showed total agreement for 588 of 590 cervical samples using the two LCR protocols (Kappa = 0.96; 95% confidence interval: 0.91-1.00). This indicates the feasibility of combined screening for C. trachomatis and squamous intraepithelial lesions using a single liquid-based cervical sample and LCR [Auguenot et al., 2001]. Pap screening may also be similarly combined with direct chlamydial antigen detection using fluorescent antibody [Inhorn et al., 2001]. Cytobrushes probably offer few advantages over a properly collected endocervical swab [Grossman et al., 1993; Wandall et al., 1998] although others disagree [Moncada et al., 1989].

Endometrium: The endometrial lining may be swabbed via the cervical os using a sleeved swab. There is a risk of introducing infection from the lower genital tract into the upper genital tract, so the method is not recommended.

Tampons and urine. These are most appropriate for self-sampling by the patient; see: non invasive sampling. With sensitive laboratory tests both sample types seem to work well.

Male genital tract

Few males seem to enjoy an endourethral swab! Fresh voided urine is the specimen of choice and is unlikely to frighten the punters off follow-up assessment.

Chlamydophila pneumoniae. 

No well validated commercial products or standardised procedures are available to guide the diagnosis of infections with this organism [Apfalter et al., 2001a]. C. pneumoniae is only rarely recovered in HL cells or Hep2 cells from the respiratory tract or cardiovascular system. The significance of C. pneumoniae as a cardiovascular pathogen is uncertain, although the presence of C. pneumoniae in peripheral mononuclear cells is likely, at best, to be undesirable [Wong, Dawkins and Ward, 1999]. Nucleic acid amplification based molecular methods for this organism are likely to be the best method of diagnosing active infection with this organism, based on nasopharyngeal swabs, washes, or, for cardiovascular infection, circulating peripheral blood mononuclear cells. Not surprisingly, peripheral blood mononuclear cells are not an appropriate specimen for the diagnosis of acute respiratory infection with C. pneumoniae [Apfalter et al., 2001b].

See also: non invasive sampling

[MEW] May 2002.

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References

Anguenot, J. L., de Marval, F., Vassilakos, P., Auckenthaler, R., Ibecheole, V. & Campana, A. (2001). Combined screening for Chlamydia trachomatis and squamous intra-epithelial lesions using a single liquid-based cervical sample. Human Reproduction 16, 2206 - 2210. [Cervical cytology plus LCR on a liquid preparation]

Apfalter, P., Blasi, F., Boman, J., Gaydos, C. A,. Kundi, M., Maass, M. et al. (2001a). Multicenter comparison trial of DNA extraction methods and PCR assays for detection of Chlamydia pneumoniae in endarterectomy specimens. Journal of Clinical Microbiology 39, 519 - 524. [Shows the huge variability in PCR detection methods for C. pneumoniae in different laboratories, presumably underlying many of the apparent contradictions in the literature]. Full article

Apfalter, P., Boman, J., Nehr, M., Hienerth, H., Makristathis, A., Pauer, J., Thalhammer, F., Willinger, B., Rotter, M. L. & Hirschl, A. M. (2001b). Application of blood-based polymerase chain reaction for detection of Chlamydia pneumoniae in acute respiratory tract infections. European Journal of Clinical Microbiology and Infectious Diseases 20, 584 - 586. [Unsurprisingly reports on a small number of patients that peripheral blood mononuclear cells are not an appropriate specimen for the diagnosis of acute respiratory infection with C. pneumoniae].

Grossman, J. H. 3rd., Rivlin, M. E & Morrison, J. C. (1993). Cytobrush versus swab endocervical sampling for the detection of obstetric chlamydial infection. American Journal of Perinatology 10, 76 - 78.[Cytobrush was associated with increased bacterial contamination].

Inhorn, S. L., Wand, P. J., Wright, T. C., Hatch, K. D., Hallum, J. & Lentrichia, B, B. (2001). Chlamydia trachomatis and Pap testing from a single, fluid-based sample. A multicenter study. Journal of Reproductive Medicine 46, 237 - 242. [DFA and Pap cytology on a liquid preparation]

Loeffelholz, M. J., Jirsa, S. J., Teske, R. K. & Woods, J. N. (2001). Effect of endocervical specimen adequacy on ligase chain reaction detection of Chlamydia trachomatis. Journal of Clinical Microbiology 39, 3838 - 3841. [Cervical samples containing endocervical cells give higher positivity rates in LCR].

Moncada, J., Schachter, J., Shipp, M., Bolan, G., Wilber, J. (1989). Cytobrush in collection of cervical specimens for detection of Chlamydia trachomatis. Journal of Clinical Microbiology 27, 1863 - 1866.

Wandall, D. A., Ostergaard, L., Overgaard, L., Worm, A. M. & Gutschik, E. (1998). Opportunistic screening for Chlamydia trachomatis cervicitis: the value of cytobrush specimens for detection by PCR compared with cell culture. APMIS 106, 580 - 584. [Cytobrush caused increased cytotoxicity for cell culture growth of C. trachomatis and had no significant advantage for PCR]. 

Wong, Y. K., Dawkins, K. D. & Ward, M. E. (1999). Circulating Chlamydia pneumoniae DNA as a predictor of coronary artery disease. Journal of the American College of Cardiology 34, 1435 - 1439. [Large study on 1300 patients indicating that the presence of circulating C. pneumoniae DNA in peripheral blood mononuclear cells was associated with greater risk of angiographic abnormalities in males].

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