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Tuesday, May 9, 2006
136

Performance of Three Nucleic Acid Amplification Tests (NAATs) for the Detection of Chlamydia trachomatis and Neisseria gonorrhoeae using Self-collected Vaginal Swabs Obtained from an Internet-based Screening Program

Billie Jo Wood, Jeff Holden, Andrew Hardick, Patricia Agreda, Nicole Quinn, Mathilda Barnes, and Charlotte Gaydos. Division of Infectious Diseases, Medicine, Johns Hopkins University, 1159 Ross Bldg, 720 Rutland Ave, Baltimore, MD, USA


Background:
An Internet-based screening program, www.iwantthekit.org, designed to educate and screen women for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG), offered home self-sampling kits.

Objective:
To evaluate the performance of three NAATs used to detect CT and NG.

Method:
From July 2004 to August 2005, 500 self-collected vaginal swabs were tested for CT and NG by Becton-Dickinson ProbeTec™ SDA, Gen-Probe® APTIMA® Combo2 TMA, and Roche Amplicor® PCR. Each swab was expressed in 800µl Tris-EDTA buffer; 200µl was placed into SDA diluent, 200µl was placed into TMA swab transport medium, and 200µl was DNA-extracted using MagNA Pure®LC. All tests were conducted according to manufacturers' procedures. The gold standard for a CT or NG infected patient was defined as >2 positive NAATs.

Result:
Of 500 swabs submitted, 46 were CT infected (9.2%), 5 NG infected (1.0%), and 3 of these were co-infected (0.6%). CT: ProbeTec had a sensitivity and specificity of 82.6% (38/46) and 100% (454/454), respectively. Combo 2 had a sensitivity and specificity of 100% (46/46) and 100% (454/454), respectively. PCR had a sensitivity and specificity of 100% (46/46) and 99.3% (451/454), respectively. GC: ProbeTec had a sensitivity and specificity of 80% (4/5) and 100% (495/495), respectively. Combo 2 had a sensitivity and specificity of 100% (5/5) and 100% (495/495), respectively. PCR had a sensitivity and specificity of 100% (5/5) and 98.8% (489/495), respectively. Overall, PCR had 3 CT false positives (0.6%) and 6 NG false positives (1.2%). Additionally, ProbeTec had 8 CT false negatives (1.6%) and one NG false negative (0.2%).

Conclusion:
Our results were consistent with the sensitivities and specificities stated by the manufacturers. Use of confirmatory testing can increase sensitivity and decrease the likelihood of false positives. Self-collected vaginal swabs appear to be suitable specimens for NAAT testing for chlamydia and gonorrhea.

Implications:
Self collected vaginal samples are suitable specimens for NAAT testing.