Real-Time Assay Evaluated for Two Sexually Transmitted Diseases

Chlamydia trachomatis and Neisseria gonorrhoeae are the two most commonly reported sexually transmitted infections (STIs) in the USA and the numbers of cases are increasing. C. trachomatis and N. gonorrhoeae infections in the rectum and pharynx are important extragenital reservoirs of infection.

Due to their high sensitivity and specificity, nucleic acid amplification tests (NAATs) have become the recommended method for detecting N. gonorrhoeae and C. trachomatis infections of the urogenital tract. The Centers for Disease Control and Prevention (CDC, Atlanta, GA, USA) recommends screening of all sexually-active men who have sex with men (MSM) for rectal C. trachomatis and N. gonorrhoeae infections and pharyngeal N. gonorrhoeae, at least annually.

Scientists from the David Geffen School of Medicine (Los Angeles, CA, USA) examined the analytical performance of the Abbott RealTime CT/NG assay (Abbott Laboratories, Abbott Park, IL, USA), including the limit of detection, inclusivity, and analytical specificity for C. trachomatis and N. gonorrhoeae in rectal and pharyngeal specimens. All tests were performed on the Abbott m2000 RealTime system. Elementary Bodies (EB)/mL for C. trachomatis and colony-forming units (CFU)/mL for N. gonorrhoeae, in clinical rectal and pharyngeal swab matrices were measured. Inclusivity was performed against 12 serovars of C. trachomatis and seven strains of N. gonorrhoeae. The analytical specificity was performed using 28 different bacteria and viruses.

The limit of detection for C. trachomatis was 2.56 EB/mL in pharyngeal specimens and 12.8 EB/mL in rectal specimens. The limit of detection for N. gonorrhoeae was 0.0256 CFU/mL for both pharyngeal and rectal specimens. The inclusivity and analytical specificity were 100% for both rectal and pharyngeal specimens. In total, there were 80 specimens tested by the second laboratory. All 40 rectal and pharyngeal specimens spiked with C. trachomatis and all 40 rectal and pharyngeal specimens spiked with N. gonorrhoeae tested positive. C. trachomatis was detected in 0/20 of the N. gonorrhoeae-spiked samples from each anatomic site and N. gonorrhoeae was detected in 0/20 C. trachomatis-spiked samples from each anatomic site.

The authors concluded that their analytical performance data demonstrate that the Abbott CT/NG RealTime assay is an accurate, sensitive, and specific assay in rectal and pharyngeal specimens, supporting the potential of the assay for detection of rectal and pharyngeal C. trachomatis and N. gonorrhoeae infections. The study was published on April 2, 2020 in The Journal of Molecular Diagnostics.