Pooling Specimens Using Gen-Probe's Aptima Combo 2 Assay For Chlamydia trachomatis and Neisseria gonorrhoeae

Background:
Molecular testing for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (GC) has become the accepted standard of care. Nucleic acid amplification tests (NAATs) detect up to 30% more positive CT specimens than non-amplified tests.

Objective:
In previous studies, pooling of samples has proven to be a useful cost-cutting tool using first generation NAATs. In this study we provide similar evidence to support the use of pooling using Gen-Probe's Aptima Combo 2 CT/GC Assay (TMA).

Method:
Four public health laboratories in Washington State, participating in the Region X Infertility Prevention Project, compared test sensitivity of 2765 cervical and urine (male and female) specimens in 619 pools of either 4 or 5 specimens per tube to the same specimens processed individually using the standard protocol for Aptima Combo 2. Individual specimen volume was reduced from 400ul per assay to 80-100ul.

Result:
198 positive CT specimens and 24 positive GC specimens were detected by both methods. Using a cut-off point of >25 RLUs to indicate a positive pool, all positive specimens detected by standard protocol were also detected by pooling. Two pools, positive for CT (530 and 585 RLUs) were negative by standard protocol. Another pool, equivocal for GC was negative by standard protocol. There were 2765 standard assays run versus 1414 assays by pooling, resulting in reagent cost savings of 49%.

Conclusion:
Pooling is an accurate and less expensive alternative to individual testing using the Aptima Combo 2 Assay. Pool size should be determined by the combined prevalence of CT/GC in the population being tested.

Implications:
Accurate and more affordable testing can be accomplished in public health populations by using pooling techniques for amplified assays.