Performance of Three Nucleic Acid Amplification Tests for Detection of
Chlamydia trachomatis
and
Neisseria gonorrhoeae
by Use of Self-Collected Vaginal Swabs Obtained via an Internet-Based Screening Program
Authors: Masek Billie Jo , Arora Nick , Quinn Nicole , Aumakhan Bulbul , Holden Jeff , Hardick Andrew , Agreda Patricia , Barnes Mathilda , Gaydos Charlotte A. 
Published: April 2009

Use of self-obtained vaginal specimens processed by nucleic acid amplification tests (NAATs) has significantly increased the utilization of nontraditional locations for
Chlamydia trachomatis
and
Neisseria gonorrhoeae
screening programs. One important emerging source of such venues includes home-based self-sampling kits available via the Internet. The objective of our study was to evaluate the performance of three commercially available NAATs (Becton-Dickinson ProbeTec SDA, Gen-Probe Aptima Combo2 TMA, and Roche Amplicor PCR) for detection of
C. trachomatis
and
N. gonorrhoeae
in vaginal samples obtained via an Internet-based screening program. From July 2004 to August 2005, 500 self-collected vaginal swabs were tested for
C. trachomatis
and
N. gonorrhoeae
by using all three NAATs. Another 500 samples were collected between August 2005 and November 2007 and tested by ProbeTec and Combo2; PCR testing was discontinued due to low specificity for
N. gonorrhoeae
. All tests were conducted according to the manufacturers' procedures; the “gold standard” for an infected
C. trachomatis
or
N. gonorrhoeae
patient was defined as ≥2 positive NAAT results. Of the first 500 swabs submitted, 46 were
C. trachomatis
infected (9.2%) and 5 were
N. gonorrhoeae
infected (1.0%), and 3 of these were coinfected (0.6%). All
C. trachomatis
and
N. gonorrhoeae
Combo2-positive/ProbeTec-negative samples were confirmed as true positives by an alternative NAAT. For
C. trachomatis
, ProbeTec, Combo2, and PCR had sensitivities of 82.6%, 100%, and 100%, with specificities of 100%, 100%, and 99.3%, respectively. For
N. gonorrhoeae
, ProbeTec, Combo2, and PCR had sensitivities of 80%, 100%, and 100%, with specificities of 100%, 100%, and 98.8%, respectively. Of the total 1,000 swabs submitted, 92 were
C. trachomatis
infected (9.2%) and 15 were
N. gonorrhoeae
infected (1.5%), and 7 of these were coinfected (0.7%). There were no ProbeTec-positive/Combo2-negative samples. For
C. trachomatis
, ProbeTec and Combo2 had sensitivities of 81.5% and 100%, with specificities of 100% and 100%, respectively. For
N. gonorrhoeae
, ProbeTec and Combo2 had sensitivities of 80% and 100%, with specificities of 100% and 100%, respectively. Overall, ProbeTec had 17
C. trachomatis
false-negative results (1.7%) and 3
N. gonorrhoeae
false-negative results (0.3%), while Combo2 had none. Our results were consistent with the sensitivities and specificities stated by the manufacturers. NAATs perform well for detection of chlamydia and gonorrhea with self-obtained vaginal swabs shipped in a dry state to a laboratory. For 1,000 self-collected vaginal swabs tested by NAATs, the sensitivities for
C. trachomatis
and
N. gonorrhoeae
for Combo2 were 100% and 100%, while they were 81.5% and 80%, respectively, for ProbeTec. For 500 PCR samples, the
C. trachomatis
sensitivity was 100% and the
N. gonorrhoeae
sensitivity was 100%, with specificities of 99.3% and 98.8%, respectively.