| The
Digene Hybrid Capture 2 CT/GC, CT-ID, and GC-ID DNA tests perform as well
as or better than culture for the detection of C. trachomatis and N.
gonorrhoeae in cervical specimens.
Comparison of
Digene Hybrid Capture 2 and conventional culture for detection of
Chlamydia trachomatis and Neisseria gonorrhoeae in cervical specimens.
Darwin LH, Cullen AP, Arthur PM, Long CD,
Smith, KR, Girdner JL, Hook EW III, Quinn TC, Lorincz AT.
Jornal of Clinical Microbiology 2002;40:641-644.
Summary:
Question
Does the Hybrid Capture 2 CT/GC test algorithm perform better than culture
for the detection of C. trachomatis and N. gonorrhoeae in
cervical specimens from high-risk populations?
Design
This study describes a blinded comparison of the results from the Hybrid
Capture 2 (HC2) CT/GC, CT-ID, and GC-ID DNA tests with those of
conventional C. trachomatis and N. gonorrhoeae cultures of
cervical swab specimens. The HC2 testing algorithm included analyzing all
specimens first using the combined CT/GC test. All CT/GC positive samples,
all samples showing discrepancies between CT/GC and culture results, all
specimens within 30% of the CT/GC cutoff, and an equal number of negative
samples were then retested by using both the CT-ID and the GC-ID tests.
Participants
Six hundred sixty-nine women from high-risk female populations attending
sexually transmitted disease clinics in Birmingham, AL and Baltimore, MD,
were studied.
Description of Tests and Diagnostic
Standard
Three cervical specimens were collected from each patient. The first was a
swab for gonococcal culture, inoculated onto modified Thayer-Martin medium
and cultured using conventional methods. The second and third specimens
were a swab for chlamydial cell culture and a cervical brush placed into
specimen transport medium for HC2, with the order of collection alternated
between patients. Using the HC2 testing algorithm described above, all
brush samples were tested with the HC2 CT/GC assay (Digene Corporation,
Gaithersburg, MD) and approximately 55% were analyzed using the CT-ID and
GC-ID test kits (Digene Corporation). Specimens that tested positive by
the CT/GC test and whose results were then confirmed or identified by the
CT-ID and/or the GC-ID test were considered positive for the specific
organism identified.
Main Outcome Measures
The sensitivity, specificity, positive predictive value (PPV), and
negative predictive value (NPV) of the HC2 testing algorithm for the
detection of C. trachomatis and N. gonorrhoeae as measured
by conventional culture methods for each organism were determined.
Main Results
Among the 669 clinical specimens evaluated, 58 were culture-positive for C.
trachomatis and 72 were culture-positive for N. gonorrhoeae.
Eighteen were positive for both organisms. Of the 112 culture-positive
specimens, the HC2 CT/GC test detected 105 and found 23 positive specimens
that were not detected by culture, for a sensitivity and specificity of
detection of C. trachomatis or N. gonorrhoeae by the HC2
CT/GC assay of 93.8% and 95.9%, respectively, compared to culture. A
comparison of HC2 CT-ID and GC-ID test performances compared to culture is
shown in the table. The specificity of the culture was 100% by definition.
The CT-ID test was slightly more sensitive in detecting chlamydiae than
the GC-ID test was in detecting gonococci.
| Comparison
of HC2 CT-ID and GC-ID test performance* to culture |
| HC2 CT-ID |
96.6 |
96.9 |
74.7 |
99.7 |
| HC2 GC-ID |
90.3 |
98.5 |
77.4 |
98.8 |
| *A total of 367
specimens were examined by both the CT-ID and GC-ID tests. The data
analyses were based on the algorithm results and 669 specimens
tested by the CT/GC kit. |
Authors' Conclusions
The HC2 CT/GC DNA test is a reliable and
rapid method for detection of C. trachomatis and N. gonorrhoeae
simultaneously from a single specimen and is useful for screening in
low-prevalence populations.
Source of funding: None given
For correspondence: Allison Cullen,
Digene Corporation, 1201 Clopper Rd, Gaithersburg, MD 20878. E-mail
address: allison.cullen@digene.com.
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