Question
How well do the APTIMA transcription mediated amplification assays (TMA) perform compared to ligase chain reaction, culture, and fluorescent antibody assays for the detection of C. trachomatis and N. gonorrhoeae in urine and urogenital swab samples from men and women? Can the APTIMA CT and GC assays be used as confirmatory tests for specimens positive by the APTIMA Combo 2 assay?
Design
The results of the APTIMA Combo 2 assay (AC2) were compared to the results of ligase chain reaction (LCx) and culture for C. trachomatis and N. gonorrhoeae, and fluorescent antibody (DFA) for C. trachomatis, performed on urogenital swab or urine specimens from men and women. The results of the APTIMA CT (ACT) and GC (AGC) assays were compared to those of the AC2 assay to evaluate their usefulness to confirm AC2-positive results.
Participants
First-catch urine or urogenital swab specimens (n = 1304) were collected from male and female patients, including 710 for C. trachomatis detection by LCx (n = 516), DFA (n= 109), or culture (n = 85) and 594 for N. gonorrhoeae detection by LCx (n = 510) or culture (n = 84).
Description of Tests and Diagnostic Standard
Specimen collection was performed with the appropriate swab type for each assay. Swab specimens were tested for C. trachomatis and N. gonorrhoeae by culture performed according to standard operating procedures and by the LCx CT and GC assays (Abbott) performed according to the package insert. Swab specimens were tested for C. trachomatis by DFA performed by the Bartels chlamydiae fluorescent monoclonal antibody test. Urine specimens were tested only by the LCx CT and GC assays. Specimens were stored at 4oC for an average of 2 weeks before they were transferred into AC2 specimen collection tubes and tested by AC2 (Gen-Probe) according to the kit insert and for up to 60 days before testing with ACT or AGC (Gen-Probe). All 1304 specimens were tested by AC2; 675 specimens (253 urines and 422 swabs) were tested by ACT (n = 361) or AGC (n = 314), based on the availability of sufficient sample volume. AC2-positive specimens were tested twice by AC2.
The AC2 is a US FDA-approved TMA assay for the simultaneous detection of C. trachomatis and N. gonorrhoeae in endocervical or male urethral swabs, vaginal swabs, and urine specimens, which amplifies a region of the 23S rRNA of C. trachomatis and the 16S rRNA of N. gonorrhoeae. The ACT and AGC are TMA tests that target different C. trachomatis and N. gonorrhoeae 16S rRNA sequences than AC2.
Main Outcome Measures
The results of C. trachomatis and N. gonorrhoeae detection by LCx, culture, DFA, and AC2 in a total of 1304 urine and swab specimens from men and women were compared. The concordance between the results of the AC2, and the ACT and AGC assays for C. trachomatis and N. gonorrhoeae detection in 675 specimens was determined.
Main Results
The results of culture, DFA, LCx, and AC2 for detection of C. trachomatis or N. gonorrhoeae in a total of 1304 urine and swab specimens are shown in the table. All AC2-positive specimens were positive on repeat analysis. There was 100% concordance between the results of AC2 and ACT and AGC for the subset of 675 specimens tested by either assay. LCx did not detect 1 of 14 ACT-positive and 1 of 6 AGC-positive urine specimens and yielded 1 C. trachomatis and 1 N. gonorrhoeae-positive result for swab specimens not confirmed by ACT and AGT, respectively. Culture did not detect 6 of 21 ACT and 3 of 4 AGC-positive specimens. DFA did not detect any of 4 ACT-positive specimens.
Detection of C. trachomatis and N. gonorrhoeae in a total of 1304 urine and swab specimens by AC2, LCx, culture and DFA.
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Test method
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Number of specimens with positive result/number tested (%)
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C. trachomatis
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N. gonorrhoeae
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|
AC2
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79/710 (11.1)
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23/594 (3.9)
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|
LCx
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45/516 (8.7)
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18/510 (3.5)
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|
Culture
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16/85 (18.8)
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1/84 (1.2)
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|
DFA
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0/109 (0)
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NT*
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* not tested
Authors‚ Conclusions
The correlation of the APTIMA assays with LCx was good, while the sensitivity of culture and DFA compared to AC2 was significantly lower. The ACT and AGC assays demonstrated absolute concordance with the AC2 test for detection of C. trachomatis and N. gonorrhoeae in urine and swab samples. The APTIMA assay performance was not altered when using LCx, culture, or DFA swabs that were transferred after 2 weeks to the APTIMA-specific transport tubes rather than the specific collection swabs provided by Gen-Probe.
Source of funding: Specialty Laboratories, Inc., Santa Monica, CA and Gen-Probe Incorporated, San Diego, CA.
For correspondence: B. Boyadzhyan, Specialty Laboratories, Santa Monica, CA 90404. E-mail address:
bboyadzhyan@specialtylabs.com.
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