Comparison of Roche Cobas Amplicor and Abbott LCx for the rapid detection of Chlamydia trachomatis in specimens from high-risk patients

[Up to date in sexually transmitted infections: epidemiology, diagnostic approaches and treatments]

In the last years, there have been important advances in sexually transmitted infections such as genome sequencing of Treponema pallidum, Chlamydia trachomatis or Mycoplasma genitalium; the new taxonomic position of Calymmatobacterium granulomatis; commercial diagnostic systems based on nucleic acid amplification; the emergence of quinolone resistance in Neisseria gonorrhoeae; new therapeutic approaches in vulvovaginal candidiasis that include boric acid; the demonstration that valacyclovir reduces the risk of transmission of genital herpes or the availability of immune-response modifier in the treatment of genital warts, and that are questions in the goal of this review. Viral hepatitis and HIV were no reviewed by space reasons.

Cost-Effectiveness Analysis of Screening Adolescent Males for Chlamydia On Admission to Detention

BACKGROUND

Chlamydia trachomatis infections can lead to serious and costly sequelae. Because chlamydia is most often asymptomatic, many infected youth do not seek testing. Entry to a detention system provides an opportunity to screen and treat many at-risk youth. GOAL The goal of this study was to determine the cost-effectiveness of screening male youth for chlamydia on entry to detention.

STUDY DESIGN

Incremental cost-effectiveness of 3 chlamydia screening strategies was compared for a hypothetical cohort of 4000 male youth per year: 1) universal chlamydia screening using a urine-based nucleic acid amplification test (NAAT), 2) selective NAAT screening of urine leukocyte esterase (LE)-positive urines, and 3) no screening. The model incorporated programmatic costs of screening and treatment and medical cost savings from sequelae prevented in infected males and female partners. The analysis was conducted from the healthcare system perspective.

RESULTS

Chlamydia prevalence in the sampled population of 594 was 4.8%, and the average number of female sexual partners/infected male was 1.6. Universal NAAT screening was the most cost-effective strategy, preventing 37 more cases of pelvic inflammatory disease (PID) and 3 more cases of epididymitis than selective screening and saving an additional 24,000 dollars. The analysis was sensitive to NAAT cost, LE sensitivity, rate of PID development, PID sequelae cost, and number of female partners. Universal screening remained the most cost saving for prevalence as low as 2.8% or higher.

CONCLUSIONS

Universal chlamydia screening of adolescent males on entry to detention was the most cost-effective strategy. Savings are primarily the result of the prevention of PID in recent and future partners of index males. Screening detained male youth using a urine-based NAAT provides a public health opportunity to significantly reduce chlamydia infections in youth at risk for sexually transmitted diseases.

Efficacy of an RNA detection test kit in the diagnosis of genital chlamydial infection

A nucleic acid amplification method based on DNA detection, the current standard method for the diagnosis of genital infection by Chlamydia trachomatis, has been shown to potentially yield false-positive results after treatment in the clinical setting. RNA detection methods are more appropriate because viable organisms have multiple RNA copies that are surely detected by the method. In this study, we evaluated the efficacy of a new RNA detection test kit, the VIDAS PROBE CT test, in the diagnosis of genital chlamydial infection. For comparison, the standard DNA detection method, Amplicor STD-I, was also used in the study. First voided-urine samples and urethral smears from male patients with urethritis, and first voided-urine samples and cervical smears from female patients with cervicitis served as samples for the detection of C. trachomatis. Of the 60 first voided-urine samples from male patients, 21 were positive and 39 negative with the VIDAS PROBE CT test. Amplicor STD-I achieved exactly the same result. In female patients with cervicitis, the two test kits produced the same result, with 2 positive cervical smears and 38 negative. These results suggest that the VIDAS PROBE CT test is as efficient as Amplicor STD-I in the detection of C. trachomatis. While studies including a greater number of patients will be needed for revealing the unique advantages of the new RNA detection test kit, VIDAS PROBE CT, we concluded from the current study that the test may be clinically useful in the diagnosis of genital chlamydial infection.

Confirmation by 16S rRNA PCR of the COBAS AMPLICOR CT/NG test for diagnosis of Neisseria gonorrhoeae infection in a low-prevalence population

The COBAS AMPLICOR CT/NG test is widely used for the diagnosis of Neisseria gonorrhoeae infection using genital swabs or urine samples. Although highly specific, cross-reactivity occurs with some nonpathogenic strains of Neisseria and Lactobacillus species. In low-prevalence populations, even highly specific assays may require confirmatory testing of positive results. We assessed the positive predictive value (PPV) of this test in a low-prevalence (0.5%) setting. Genital and urine specimens testing positive using the COBAS AMPLICOR NG test were retested using an investigational 16S rRNA PCR assay. Additionally, 737 specimens were tested in parallel by both culture and the above PCR protocol. Of 9,772 specimens tested in-house, 168 were positive by the AMPLICOR test; in addition, 62 AMPLICOR-positive specimens were referred to our laboratory for confirmatory testing, yielding 230 positive specimens. Of these, 72 were confirmed positive by 16S rRNA PCR, yielding a specificity of 98.7% and a PPV of 31.3%. Specificity was similar for all specimen types, whereas PPV varied with prevalence: specimens from males, females, urine specimens, and genital swabs had PPVs of 70.8, 13.3, 51.9, and 20.1%, respectively. The PPV was higher when the initial AMPLICOR optical density (OD) was > or =3.5 versus initial and repeat OD readings in an equivocal zone of > or =0.2 to <3.5 (65.1 versus 10.1%; P < 0.001). On repeat testing of specimens with ODs in the equivocal zone, 54 gave ODs of > or =0.2 and <2.0, 35 gave ODs of > or =2.0 and <3.5, and 12 gave ODs of > or =3.5, with 3.7, 20, and 33.3% confirmed positive, respectively (P = 0.004). Comparing PCR to culture as the "gold standard," specificity increased from 96.8 to 99.9% when 16S rRNA PCR was performed on specimens positive by the COBAS AMPLICOR NG test. Confirmatory testing with a more specific method such as 16S rRNA PCR should be considered in low-prevalence populations, especially for specimens with an OD in the equivocal zone.

Evaluation of COBAS AMPLICOR (Roche): accuracy in detection of Chlamydia trachomatis and Neisseria gonorrhoeae by coamplification of endocervical specimens

We evaluated further the accuracy of the COBAS AMPLICOR (Roche) (CA) PCR-based system in detection of Chlamydia trachomatis and Neisseria gonorrhoeae in endocervical specimens. Endocervical specimens collected for any indication for testing for C. trachomatis and N. gonorrhoeae among a university hospital health system population were included. Testing for C. trachomatis was done by two PCR methods, CA and manual microwell AMPLICOR (Roche) (MWA), and by culture; testing for N. gonorrhoeae was done by CA and culture. Discrepancy resolution was performed. Reproducibility testing and hands-on labor time measurements for CA were done. Among 654 C. trachomatis samples, the prevalence of true positivity was 9.2%, and among the 618 N. gonorrhoeae samples, the prevalence of true positivity was 4.4%. For detection of C. trachomatis, the sensitivity, specificity, and negative and positive predictive values were, respectively, as follows for each test: CA, 93.3, 99.7, 99.3, and 96.4%; MWA, 91.7, 99.7, 99.2, and 96.5%; and culture, 65.0, 100, 96.6, and 100%. For detection of N. gonorrhoeae those values were as follows: CA, 96.3, 100, 99.8, and 100%; and culture, 92.6, 100, 99.7, and 100%. Hands-on labor time for each clinical result was estimated to be at 7.5 min. The prevalence of inhibitory specimens was 3.5%, including two positive C. trachomatis samples which would have been missed otherwise. The direct cost of each clinical result with CA was estimated to be $9.09. Our methods include a diverse range of indications for testing among women, using endocervical swabbing samples, 2 M sucrose phosphate transport medium, and discrepancy resolution for comparison. Under our test conditions, the CA system is an accurate, rapid, and cost- and labor-efficient method for detection of C. trachomatis and N. gonorrhoeae.

Detection of Chlamydia trachomatis and Neisseria gonorrhoeae by enzyme immunoassay, culture, and three nucleic acid amplification tests

The purpose of this study was to evaluate and compare three commercially available nucleic acid amplification tests (NAATs) for the detection of Neisseria gonorrhoeae and Chlamydia trachomatis. Roche PCR and Becton Dickinson strand displacement amplification (SDA) were performed on 733 endocervical swab specimens from commercial sex workers. Abbott ligase chain reaction (LCR) was performed on a subset of 396 samples. Endocervical specimens from all women were also tested by culture for N. gonorrhoeae and by Syva MicroTrak enzyme immunoassay (EIA) for C. trachomatis. A positive N. gonorrhoeae result was defined as a positive result by culture or by two NAATs, and a positive C. trachomatis result was defined as a positive result by two tests. According to these definitions, the sensitivities and specificities for the subsample of 396 specimens of N. gonorrhoeae culture, PCR, SDA, and LCR were 69.8, 95.2, 88.9, and 88.9% and 100, 99.4, 100, and 99.1%, respectively; the sensitivities and specificities of C. trachomatis EIA, PCR, SDA, and LCR were 42.0, 98.0, 94.0, and 90.0% and 100, 98.0, 100, and 98.6%, respectively. The performance characteristics of N. gonorrhoeae culture, PCR, and SDA and C. trachomatis EIA, PCR, and SDA for all 733 specimens were defined without inclusion of LCR results and by discrepant analysis after resolution of discordant N. gonorrhoeae PCR results and of discordant C. trachomatis EIA and PCR results by LCR testing. The sensitivities of N. gonorrhoeae culture, PCR, and SDA before and after LCR resolution were 67.8, 95.7, and 93.9% and 65, 95.8, and 90.0%, respectively. The sensitivities of C. trachomatis EIA, PCR, and SDA decreased from 39.4, 100, and 100% to 38.7, 98.7, and 94.7%, respectively. All three NAATs proved to be superior to N. gonorrhoeae culture and to C. trachomatis EIA. The accuracies of the different NAATs were quite similar. SDA was the only amplification assay with 100% specificity for detection of both N. gonorrhoeae and C. trachomatis in endocervical specimens.

Evaluation of the NucliSens Basic Kit for detection of Chlamydia trachomatis and Neisseria gonorrhoeae in genital tract specimens using nucleic acid sequence-based amplification of 16S rRNA

We evaluated a new RNA amplification and detection kit, the NucliSens Basic Kit (Organon Teknika), for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae in genitourinary specimens. The Basic Kit provides an open platform for RNA amplification and detection and contains isolation reagents for nucleic acid extraction, nucleic acid sequence-based amplification (NASBA) reagents (enzymes and buffers), and a generic ruthenium-labeled probe for electrochemiluminescent (ECL) detection of amplified product. Using freshly purified and titrated stocks of C. trachomatis and N. gonorrhoeae and in vitro-generated RNA transcripts for sensitivity determinations, the Basic Kit detected 1 inclusion-forming unit of C. trachomatis, 1 CFU of N. gonorrhoeae, and 100 RNA molecules of 16S rRNA for both bacteria. The clinical performance of the Basic Kit was evaluated by testing a total of 250 specimens for N. gonorrhoeae by culture and NASBA and a total of 96 specimens for C. trachomatis by PCR and NASBA. The Basic Kit detected 139 of 142 N. gonorrhoeae culture-positive specimens and gave a negative result for 73 of 74 culture-negative specimens, for a sensitivity and specificity of 97.9 and 98.7%, respectively. For C. trachomatis, the Basic Kit detected 24 of 24 PCR-positive specimens and gave a negative result for 71 of 72 PCR-negative specimens, for a sensitivity and specificity of 100 and 98.6%, respectively. The Basic Kit also detected specimens containing both N. gonorrhoeae and C. trachomatis, using a multiplex NASBA assay using primers for both bacteria. The NucliSens Basic Kit offers a versatile platform for the development of sensitive RNA detection assays for sexually transmitted diseases.

Multicenter evaluation of AMPLICOR and automated COBAS AMPLICOR CT/NG tests for Neisseria gonorrhoeae

The fully automated COBAS AMPLICOR CT/NG and semiautomated AMPLICOR CT/NG tests were evaluated in a multicenter trial for their ability to detect Neisseria gonorrhoeae infections. Test performance compared to that of culturing was evaluated for 2,192 matched endocervical swab and urine specimens obtained from women and for 1, 981 matched urethral swab and urine specimens obtained from men. Culture-negative, PCR-positive specimens that tested positive in a confirmatory PCR test for an alternative target sequence within the N. gonorrhoeae 16S rRNA gene were considered to be true positives. The overall prevalences of gonorrhea were 6.6% in women and 20.1% in men. The COBAS AMPLICOR and AMPLICOR formats yielded concordant results for 98.8% of the specimens and exhibited virtually identical sensitivities and specificities. The results that follow are for the COBAS AMPLICOR format. With the infected patient as the reference standard, the resolved sensitivities of PCR were 92.4% for endocervical swab specimens and 64.8% for female urine specimens. There were no significant differences in these rates between women with and without symptoms. Among symptomatic men, COBAS AMPLICOR sensitivities were 94.1% for urine and 98.1% for urethral swabs; for asymptomatic men, the results were 42.3 and 73.1%, respectively. In comparison, the sensitivities of culturing were 84.8% for endocervical specimens, 92.7% for symptomatic male urethral specimens, and only 46.2% for urethral specimens obtained from asymptomatic men. When PCR results were analyzed as if only a single test had been performed on a single specimen type, the resolved sensitivity was always higher. The resolved specificities of PCR were 99.5% for endocervical swab specimens, 99.8% for female urine specimens, 98.9% for male urethral swab specimens, and 99.9% for male urine specimens. The internal control revealed that 2.1% of specimens were inhibitory when initially tested. Nevertheless, valid results were obtained for 99.2% of specimens because 60.0% of the inhibitory specimens were not inhibitory when a second aliquot was tested. The COBAS AMPLICOR CT/NG test for N. gonorrhoeae exhibited high sensitivity and specificity with urethral swab and urine specimens from men and endocervical swab specimens from women and thus is well suited for diagnosing and screening for N. gonorrhoeae infection.

Multicenter evaluation of the AMPLICOR and automated COBAS AMPLICOR CT/NG tests for detection of Chlamydia trachomatis

The fully automated COBAS AMPLICOR CT/NG and semiautomated AMPLICOR CT/NG tests were evaluated in a multicenter trial for the ability to detect Chlamydia trachomatis infections. Test performance compared to that of culture was evaluated for 2,236 matched endocervical swab and urine specimens obtained from women and for 1,940 matched urethral swab and urine specimens obtained from men. Culture-negative, PCR-positive specimens that tested positive in a direct fluorescent-antibody test or in a confirmatory PCR test for an alternative target sequence were resolved as true positives. The overall prevalences of chlamydia were 2.4% in women and 7.2% in men. The COBAS AMPLICOR and AMPLICOR formats yielded concordant results for 98.1% of the specimens. With the infected patient as the reference standard, the resolved sensitivities of COBAS AMPLICOR were 89.7% for endocervical swab specimens, 89.2% for female urine specimens, 88.6% for male urethral swab specimens, and 90.3% for male urine specimens. When results were analyzed as if only a single test had been performed on a single specimen type, the resolved sensitivity was always higher. The resolved specificities of PCR were 99.4% for endocervical swab specimens, 99.0% for female urine specimens, 98.7% for male urethral swab specimens, and 98.4% for male urine specimens. The internal control revealed that 2.4% of the specimens were inhibitory when initially tested. Nevertheless, valid results were obtained for 98.6% of the specimens because 59.1% of the inhibitory specimens were not inhibitory when a second aliquot was tested. The COBAS AMPLICOR and AMPLICOR CT/NG tests for C. trachomatis exhibited equally high sensitivity and specificity with both urogenital swab and urine specimens and thus are well suited for screening for C. trachomatis infection.

The Use of Molecular Techniques for the Diagnosis and Epidemiologic Study of Sexually Transmitted Infections

Molecular diagnostic tests are more sensitive and, in many cases, more specific than conventional laboratory methods for the detection of sexually transmitted infections. Here, we review recently developed molecular methods for the diagnosis and subtyping of the most common sexually transmitted infections: infections caused by Chlamydia trachomatis, Neisseria gonorrhoeae, human papillomavirus, Trichomonas vaginalis, and the agents of genital ulcer disease (Haemophilus ducreyi, herpes simplex virus, Treponema pallidum, and Calymmatobacterium granulomatis). We also provide an overview of the laboratory diagnostic tests and clinical specimens to use when infection with these agents is suspected.

Determination of Chlamydia trachomatis prevalence in an asymptomatic screening population: performances of the LCx and COBAS Amplicor tests with urine specimens

This study determined the performances of the LCx (Abbott) and COBAS Amplicor (Roche) tests with urine specimens for the detection of Chlamydia trachomatis in an asymptomatic screening population. Randomly selected women and men (age range, 15 to 40 years) registered in 20 general practices in Amsterdam, The Netherlands, were invited to participate in this study. Urine specimens (n = 2, 906; 1,138 specimens from men and 1,717 specimens from women) were tested for C. trachomatis by the COBAS Amplicor (Roche) and LCx (Abbott) tests. Samples which were positive by only one assay were subjected to discrepant analyses by a third assay (in-house plasmid PCR). By the LCx assay C. trachomatis DNA was detected in urine specimens from 46 of 1,717 women and 29 of 1,138 men, while the COBAS Amplicor detected C. trachomatis DNA in 52 and 35 specimens, respectively. When comparing the LCx and COBAS Amplicor tests, 32 test results (20 for women and 12 for men) were discrepant. After discrepant analyses the following sensitivities, specificities, and positive predictive values were found for the LCx and COBAS Amplicor tests: 78.6 versus 98.8%, 99.7 versus 99.9%, and 88.0 versus 95.4%, respectively. No prominent differences were found between men and women with regard to the test performances. After discrepant analyses the overall prevalences of C. trachomatis in women and men were 3.0 and 2.8%, respectively. For both women and men the prevalence in the younger age groups was higher than that in the older age groups. In conclusion, the COBAS Amplicor tests shows better diagnostic characteristics than the LCx assay for the detection of C. trachomatis in urine specimens from an asymptomatic screening population. In this asymptomatic population the overall prevalence of C. trachomatis was 2.9%.

Evaluation of AMPLILINK software for the COBAS AMPLICOR system

The use of AMPLILINK version 1.0 software was evaluated for the operation and control of one COBAS AMPLICOR instrument and for two COBAS AMPLICOR instruments run simultaneously to perform and detect nucleic acid amplification reactions. A total of 3,384 results were analyzed. The initial accuracy of the results was 99.91%. Three errors of omission of transfer of data from the COBAS AMPLICOR to the AMPLILINK system were observed. Two of these errors were from a single specimen, where both the analyte and internal control results were not transmitted. These errors did not interfere with the correctness of any other data. There were no interruptions of runs, and no data were mixed. AMPLILINK increased convenience, saved labor, and was found to be a very useful addition for clinical laboratories performing molecular-diagnostic procedures with the COBAS AMPLICOR system.