Literature review > Issue_5 > Review on Golden et al. 

Bacterial sexually transmitted infections (STIs) including Chlamydia trachomatis and Neisseria gonorrhoeae in men who have sex with men (MSM) are an important public health concern as the early detection and treatment may avoid transmission to sexual partners, serious sequelae, or STI-facilitated HIV transmission. Screening for asymptomatic infections by offering routine screening of extragenital sites for STIs by nucleic acid amplification tests (NAATs) is one way to control and reduce the disease burden. Clinicians often enquire if samples taken from these sites can be tested for detection of STIs and since most commercial NAATs have not been validated for use with extragenital specimens, most laboratories will not perform such testing on these samples. It is therefore important to evaluate testing of such specimens by NAATs.

Golden et al. reports on pilot data where some of the laboratory aspects, in particular sample processing, are evaluated prior to amplification by the PCR as performed by Roche COBAS Amplicor and Abbott ligase chain reaction (LCR). Although the number of positive samples evaluated are limited, nevertheless, this study provides data supporting the use of both PCR and LCR for detection of chlamydial infections in rectal samples. While minor differences in results were observed with various specimen processing methods, the study concluded that all methods gave similar results. However DNA extraction of samples gave the best results. DNA extraction, although it incorporates an extra step, is important for removal of the majority of inhibitory material. Non-conventional samples may need to undergo such extraction steps in order to ensure appropriate removal of inhibitory substances and confidence in the results [1]. Inclusion of a synthetic internal control in COBAS PCR allows for detection of inhibition in samples, however LCR does not include such controls and it might not be practical and cost efficient to dilute every sample to determine sample inhibition. However LCR has been withdrawn in most countries and is not in use in laboratories and therefore this may not be an issue.

Even if samples are not inhibitory, one aspect that may need to be explored is whether anorectal samples have been collected adequately. Examination of such sample adequacy can be performed by detection of host cell DNA, for example the beta-globin gene, which is present at one copy per cell, by PCR [2]. This may be especially important in anorectal samples where adequacy of sample collection has not been explored in large studies.

A recent study by Lister et al. [3] also performed validation of extragenital samples from asymptomatic men by COBAS PCR for amplification of the C. trachomatis omp1 gene. This evaluation was done on a larger number of positive specimens and demonstrated 94% confirmation, which is in line with the findings of Golden et al. The study by Lister et al. utilized self-collected anal swabs. Self-collection of anal swabs could improve compliance, as samples are collected in the privacy of the patient's home and sent to laboratories for testing.

Testing of anorectal samples by NAATS would also allow for performing genotyping in order to determine circulating strains in the population. This aspect was recently shown to have important public health aspects as an outbreak of serovar L2 (etiological agent of lymphogranuloma venereum) in Dutch MSMs was demonstrated [4].

Until large trials, including large numbers of asymptomatic men, are performed, commercial companies will not endorse testing of extragential samples. Nevertheless, based on the few studies published so far, NAATs, including COBAS Amplicor, seem to be adequate for detection of Chlamydial infections in anorectal samples.

References:

1. Tabrizi SN, Chen S, Cohenford MA et al. Evaluation of real time polymerase chain reaction assays for confirmation of Neisseria gonorrhoeae in clinical samples tested positive in the Roche Cobas Amplicor assay. Sex Trans Infect. 2004;80:68-71.

2. Bauer BA, Ting Y, Greer CE, Chambers et al. Manos MM. Genital human papillomavirus infection in female university students as determined by a PCR-based method. JAMA 1991; 265:472-477.

3. Lister NA, Tabrizi SN, Fairley CK, Garland SM. Validation of Roche COBAS Amplicor Assay for Detection of Chlamydia trachomatis in Rectal and Pharyngeal Specimens by an omp1 PCR Assay. J Clin Microbiol 2004; 42:239-41.

4. Nieuwenhuis RF, Ossewaarde JM, Gotz HM et al. Resurgence of Lymphogranuloma Venereum in Western Europe: An Outbreak of Chlamydia trachomatis Serovar L2 Proctitis in The Netherlands among Men Who Have Sex with Men. CID 2004; 39:996-1003.

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