Literature review > Issue 8 > Review on Lister et al. 

STD guidelines have routinely recommended screening of extragenital sites (pharyngeal and rectal) for Neisseria gonorrhoeae and Chlamydia trachomatis using conventional culture tests. However, over the past several years, screening for these STIs is often carried out by nucleic acid amplification tests (NAATs) due to the increased sensitivity and specificity of these assays even when compared to culture and other non-amplified tests. While NAATs are recommended as screening tests for gonorrhea and chlamydia, most commercial NAATs have not been validated for use with extragenital specimens. The investigators in this publication sought to investigate the utility of the commercial COBAS AMPLICOR PCR assay as a screening test for chlamydia in men who have sex with men (MSM) using a confirmatory PCR assay designed to detect the major outer membrane protein (MOMP) of chlamydia present in the COBAS AMPLICOR positive rectal and pharyngeal specimens.

A total of 52 C. trachomatis-positive swabs by COBAS AMPLICOR PCR were collected from 43 men (47 anal swabs and 5 throat swabs). Eight men testing positive had repeat positive anal swabs collected before treatment and one man had a C. trachomatis detected from both anal and throat swabs. The throat and anal swabs collected from 15 men testing C. trachomatis-negative were also included as negative controls. Three anal swabs were positive by AMPLICOR and negative by OMP1 PCR. All three were positive for β-globulin amplification. One patient who had an OMP1-negative anal sample also had C. trachomatis detected from a urine sample that was collected at the same time and was positive for C. trachomatis by both AMPLICOR and OMP1 PCRs.

In summary, this study demonstrated the reliability of utilizing the COBAS AMPLICOR PCR for detection of C. trachomatis in extragenital sites, and its overall utility as a screening assay for chlamydia among men who have sex with men. Overall, 94% of the COBAS AMPLICOR-positive samples were confirmed, and the rate may have been even higher since one of the negative anal samples was from an individual who was positive by both assays for chlamydia in urine. Thus, the three COBAS AMPLICOR-positive and OMP1 PCR-negative anal samples may not have represented false positives but could have contained bacterial levels that were below the detection of the OMP1 PCR assay. The COBAS AMPLICOR PCR assay targets the plasmid gene, which may be ten times more abundant than the MOMP gene per organism load. Thus, based on this study and others, it would be appropriate to screen for chlamydia by NAATs in both genital and extragenital specimens. The public health significance of this study is therefore quite important since NAATs are widely available in contrast to the lack of availability of standard culture for chlamydia in many public health laboratories. Furthermore, the NAATs are less expensive, less time-consuming, and more readily available than culture.

about SDI | newsletters | grants | publications | literature reviews

WHO Home - WHO Search - TDR Home - SDI Home - SDI Contact us
(c) WHO/OMS 2001