Literature reviews  >  Articles for review > Chernesky et al. Ability of new APTIMA CT and APTIMA GC ... 

The APTIMA CT and APTIMA GC nucleic acid amplification assays performed on noninvasive specimens should be suitable for screening male populations.

Ability of new APTIMA CT and APTIMA GC assays to detect Chlamydia trachomatis and Neisseria gonorrhoeae in male urine and urethral swabs.
Chernesky MA, Martin DH, Hook EW, Willis D, Jordan J, Wang S, Lane JR, Fuller D, Schacter J.
Journal of Clinical Microbiology 2005;43:127-131.
 
Summary:

Question

How well do the APTIMA CT and the APTIMA GC nucleic acid amplification tests (NAAT) perform for the detection of C. trachomatis and N. gonorrhoeae, respectively, compared to the APTIMA Combo 2 and ProbeTec NAAT in urethral swabs and urine specimens from men? 

Design

This paper describes a prospective multicenter study to determine the performance of the APTIMA CT (ACT) and the APTIMA GC (AGC) assays in comparison to the APTIMA Combo 2 (AC2) assay and the ProbeTec (PT) assay for C. trachomatis and N. gonorrhoeae detection in urethral swabs and urine specimens from men.  

Participants

Men (n = 1322) between the ages of 15 and 77 years (mean age = 28.5 years) from six sexually transmitted disease clinics in Hamilton, Ontario, Canada, New Orleans, LA, Birmingham, AL, Jacksonville, FL, Pittsburgh, PA, and San Francisco, CA, with a complete specimen set, were tested.Men were eliminated if they had urinated within 1 h of specimen collection or had taken antibiotics within the last 21 d.Blacks represented 62.2% and whites represented 24.6% of the subjects.  

Description of Tests and Diagnostic Standard

Two urethral swabs and a first catch urine sample were obtained from each patient and were collected, transported, and tested according to the procedures described in the assay package inserts. One urethral swab and a urine aliquot were tested by the PT energy transfer amplified DNA assay (Becton Dickinson Bioscience).The other swab and a second urine aliquot were tested by each of the 3 APTIMA transcription mediated amplification assays (Gen-Probe Incorporated), including the ACT, which detects C. trachomatis, the AGC, which detects N. gonorrhoeae, and the AC2, which detects both organisms. In the APTIMA method, specific rRNA is purified and concentrated by capture on magnetic beads with covalently attached poly dT molecules using an oligonucleotide probe with sequences complementary to the target rRNA sequences and a poly dA tail.The rRNA sequences are amplified using specific primers in a transcription mediated amplification assay.The amplicons are detected by hybridization to a chemiluminescent DNA probe.The ACT and AGC amplify rRNA sequences that are different from the rRNA sequences amplified by the AC2.A patient was considered infected if both of the specimen types were positive by at least one of the AC2 or PT assays or if at least one of the two specimen types was positive in both the AC2 and PT assays.Symptomatic men included only those who reported discharge or dysuria.     

Main Outcome Measures

ACT and AGC assay results from urethral swabs and urine specimens were compared to infected patient status for determining sensitivity, specificity, and predictive values.

Main Results

Among the 1322 patients tested, 236 (17.9%) and 183 (13.9%) were infected with C. trachomatis and N. gonorrhoeae, respectively.The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the ACT and AGC assays by specimen type are shown in the table.Symptoms were reported in 141 (59.7%) of 236 infected and 435 (40%) of 1086 uninfected men. Both specimen types showed high sensitivity and specificity in symptomatic and asymptomatic patients.Among men with symptoms, the urethral swab identified 3 more C. trachomatis infected men than did urine, but the same number of N. gonorrhoeae infected men were identified by both specimen types.Among asymptomatic men, the same number of men were identified as C. trachomatis positive by each specimen type, while one more N. gonorrhoeae infected man was identified by urethral swab compared to urine specimens.  

Performance of APTIMA CT and GC assays by specimen type for 1322 men

Authors' Conclusions

The ACT and AGC assays demonstrated excellent sensitivity and specificity on urethral swabs and urine specimens compared to the infected patient status as determined using the AC2 and PT assays.Differences were minimal between the sensitivities in the symptomatic and asymptomatic groups.These data should enable the screening of men by testing their urine in these tests.  

Source of funding:None given

For correspondence:M. A. Chernesky, St. Joseph's Healthcare, Hamilton, Ontario, Canada L8N 4A6.E-mail address: chernesk@mcmaster.ca

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