Literature reviews  >  Articles for review > Van Der Pol et al. Evaluation of the Digene... 

The Hybrid Capture 2 assay combined with a semiautomated system designed for high throughput demonstrated high sensitivity and specificity for detection of C. trachomatis and N. gonorrhoeae.

Evaluation of the Digene Hybrid Capture II assay with the Rapid Capture System for detection of Chlamydia trachomatis and Neisseria gonorrhoeae.
Van Der Pol B, Williams JA, Smith NJ, Batteiger BE, Cullen AP, Erdman H, Edens T, Davis K, Salim-Hammad H, Chou VW, Scearce L, Blutman J, Payne WJ.
Journal of Clinical Microbiology 2002;40:3558-3564.
 
Summary:

Question
What is the performance of the Hybrid Capture II Assay (HC2) using the Rapid Capture System compared to the HC2 performed manually, to culture, and to PCR for detection of C. trachomatis and N. gonorrhoeae?

Design
The performance of a semiautomated system application of the signal amplification-based Hybrid Capture 2 CT/GC assay (HC2-RCS) was evaluated using prospectively collected samples tested by the HC2 assay performed manually (HC2-M), by PCR, and by culture. Additional repository samples were tested to compare only the automated and manual portions of the HC2 assay.

Participants
Three hundred fifty-four women attending an STD clinic in Indianapolis, IN, were included in the prospective comparison study. Nine hundred eleven samples from women attending an obstetrics and gynecology clinic in Porto Alegre, Brazil, who were enrolled in a study to evaluate the Hybrid Capture II HPV DNA assay, were included in the comparison of repository samples.

Description of Tests and Diagnostic Standard
Three endocervical samples were collected from each woman in the prospective study. A swab was plated on modified Thayer-Martin agar for N. gonorrhoeae culture. A brush was placed in sample transport medium (STM, Digene Corporation, Gaithersburg, MD) for the HC2 assays. A second swab was placed in chlamydia transport medium (CTM) for the C. trachomatis culture and the PCR. The order of sample collection for placement in STM and CTM was random. For the HC2 manual versus automated comparison using repository samples from Brazil, a separate endocervical sample was collected for STD diagnosis as part of the design of the original study.

N. gonorrhoeae cultures were assessed for growth for up to 48 hours. The presence of N. gonorrhoeae was confirmed if the colony was a gram-negative diplococcus, reacted to oxidase reagent, and stained positive with a fluorescent monoclonoal antibody specific for N. gonorrhoeae (Microtrak, Trinity Biotech, Ireland). Culture for C. trachomatis was performed on McCoy cells for up to 72 hours, then stained with a fluorescent monoclonal antibody specific to C. trachomatis. Specimens in CTM remaining after C. trachomatis culture were tested by PCR (COBAS Amplicor CT/NG, Roche Diagnostic Corporation, Indianapolis, IN) according to the instructions in the assay package insert.

The HC 2 CT/GC (Digene Corporation) assay was performed as a combined test for C. trachomatis and N. gonorrhoeae, followed by identification of the infecting pathogen using the CT-ID (C. trachomatis) and the GC-ID (N. gonorrhoeae) assays. An initial denaturation step was performed manually for both the HC2-M and HC2-RCS. The HC2-M was performed as described by the manufacturer. For HC2-RCS, samples were loaded on the rapid capture system, in which all assay steps prior to signal detection were performed automatically. The RCS system tests 352 samples and 32 controls during a single work shift, during which time, 3.5 h of continuous hands-free time is available for other tasks. Detection was performed in a luminometer. Relative light units (RLU) for the positive and negative controls were used to calculate a run-specific cutoff. Samples that yielded an RLU value equal to or greater than the cutoff by the CT/GC assay were retested by the CT-ID and GC-ID assays. Sample RLU values between 1 and 2.5 times the cutoff value by the CT-ID or GC-ID assay were considered equivocal and the samples were retested in duplicate. Samples were positive if the results of at least two of the three tests had RLU values equal to or greater than the cutoff.

Patients in the prospective comparison were defined as being infected if they had a positive culture result or both a positive PCR result and a positive HC2-M result.

Main Outcome Measures
The agreement between the HC2 manual and automated formats, and the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the HC2-RCS for detection of C. trachomatis and N. gonorrhoeae infections determined by culture, PCR, and HC2-M were calculated.

Main Results
In the comparison of HC2-M to HC2-RCS, positive results were obtained by HC2-M, HC2-RCS, or both assays for 62 of 354 (17.5%) and 32 of 911 (3.5%) prospective study specimens and repository specimens, respectively. Agreement was greater than 99% between assays for all samples.

For the comparison of HC2-RCS to culture and PCR, the number of subjects in the prospective study for whom samples were available for comparison of all assays was 330. The performance characteristics of the HC2-RCS, PCR, and culture for detection of chlamydial and gonococcal infections in shown in the table.

Authors' Conclusions
The availability of a high-throughput assay with excellent performance characteristics such as HC2-RCS is desirable for large clinical laboratories and may influence programmatic decisions related to screening in less traditional settings.

Source of funding: Digene Corporation

For correspondence: B. Van Der Pol, Department of Medicine, Division of Infectious Diseases, Indiana University School of Medicine, Room 435, 545 N. Barnhill Dr., Indianapolis, IN, 46202-5124. E-mail address: bvanderp@iupui.edu.

about SDI | newsletters | grants | publications | literature reviews

WHO Home - WHO Search - TDR Home - SDI Home - SDI Contact us
(c) WHO/OMS 2001