Comparison of Gen-Probe DNA probe test and culture for the detection of Neisseria gonorrhoeae in endocervical specimens

Abstract

A 2-h nonisotopic DNA probe assay for the direct detection of Neisseria gonorrhoeae in urogenital specimens has recently been modified (PACE 2; Gen-Probe, San Diego, Calif.). The new assay format was developed to increase the sensitivity of the assay and simplify procedural steps. In this study, the new DNA probe test was compared with a culture reference method for the detection of N. gonorrhoeae in endocervical specimens. The results of the DNA probe test were expressed as a ratio of relative light units (RLU) of the specimen/RLU of the cutoff recommended by the manufacturer. All patient samples with sample RLU/cutoff RLU ratios less than 0.7 were interpreted as negative, and ratios greater than 2.0 were interpreted as positive for gonorrhea. Samples with sample RLU/cutoff RLU ratios between 0.7 and 2.0 were repeated until two or more consistent negative or positive ratios were obtained. A total of 469 specimens were tested with an overall disease prevalence of 6.1%. Of the 469 patients tested, 5 specimens (1.0%) fell in this borderline region and were retested. If the manufacturer's recommended cutoff value had been used, the original DNA probe results would have resulted in two false-positives. Our data were analyzed for both symptomatic (prevalence, 11.7%) and asymptomatic (prevalence, 2%) women. The study indicated that with our modification of the manufacturer's endpoint interpretation, the DNA probe test was essentially equivalent to the culture method in terms of sensitivity, specificity, and positive and negative predictive values in both symptomatic and asymptomatic patient populations. The new DNA probe test can serve as a suitable screening and diagnostic test for the diagnosis of gonorrheal genital infections in women. Additionally, it offers the advantages of rapid turnaround time and ease of use and allows simultaneous testing for Chlamydia trachomatis on the same specimen. Gonorrhea remains one of the most important sexually transmitted diseases worldwide, with a reported 720,000 cases in the United States in 1988 (1). Gynecologic infections can range from asymptomatic to mildly symptomatic to severe, with long-term serious sequelae including infertility, chronic pelvic pain, and ectopic pregnancy. It has also been implicated in obstetric complications, neonatal pneumonia, and conjunctivitis. The control of epidemic infections and their sequelae remains dependent on correct and timely diagnosis.

Evaluation of nucleic acid-based test (PACE 2C) for simultaneous detection of Chlamydia trachomatis and Neisseria gonorrhoeae in endocervical specimens

“…After resolution of discrepant results, the PACE 2C assay had a sensitivity, a specificity, and positive and negative predictive values of 96.3, 98.8, 92.9, and 99.4%, respectively (Table 3). These values compare favorably with the results obtained from testing when single DNA probes were used (8,12,14,16,17,19). The culture sensitivities for C. trachomatis and N. gonorrhoeae in this study were 89.2 and 88.9%, respectively, suggesting that the use of culture as the reference assay, or gold standard, should be reconsidered.…”

“…Falsepositive PACE 2 assay results with low RLU values have been observed in other studies (4,8,12,14,19). Some investigators have suggested that a borderline zone for retesting of lowvalue positive or high-value negative results be developed to help in the evaluation of these samples (4,8,9,19,23,24). In using the PACE 2C assay, an intermediate zone for low-value positive results may not be needed, since all positive samples are retested by single probes to identify the organism(s).…”

Evaluation of culture and the Gen-Probe PACE 2 assay for detection of Neisseria gonorrhoeae and Chlamydia trachomatis in endocervical specimens transported to a state health laboratory

“…The possibility of being unable to culture N. gonorrhoeae because of harsh transport conditions led us to investigate the Gen-Probe system as an alternative to culture for specimens that are mailed in to the laboratory. Previous studies by Panke et al (8) have indicated the Gen-Probe test for N. gonorrhoeae is comparable to culture when specimens are processed and tested under optimal conditions for both assays. We also found that the Gen-Probe PACE 2 assay system is reliable, but the assay has the advantage of detecting many more additional positive specimens than culture does for specimens that are mailed in to the laboratory.…”

“…A system reported to be stable and accurate for detecting both N. gonorrhoeae and Chlamydia trachomatis based on DNA probes complementary to rRNA is the Gen-Probe PACE 2 assay (Gen-Probe Inc., San Diego, Calif.). This assay, which is based on a chemiluminescence detection system, has been shown to perform comparably to culture for N. gonorrhoeae and C. trachomatis detection on the basis of parallel testing of duplicate samples (4,6,8). However, prior studies involved the testing of limited numbers of specimens from local sites and did not involve significant specimen transport time.…”

Molecular genetic methods for diagnosis and characterisation of Chlamydia trachomatis and Neisseria gonorrhoeae: impact on epidemiological surveillance and interventions

“…Numerous DNA/RNA‐based noncultural methods, mainly NAATs, for the identification of N. gonorrhoeae have been developed. The PACE 2 assay (Gen‐Probe) has been used for several years to detect 16S rRNA of N. gonorrhoeae (63) by DNA probe hybridisation. Digene Hybrid Capture 2 (HC2) CT/GC including HC2 GC‐ID for N. gonorrhoeae (Digene Corporation) is a newer RNA‐probe based assay that identifies specific DNA sequences of the chromosome as well as the cryptic plasmid of N. gonorrhoeae (64).…”