Abbott RealTime CT/NG Assay with Modified Formulation that Detects the Chlamydia trachomatis Variant Containing a 377 bp Cryptic Plasmid Deletion

Background:
A new variant of Chlamydia trachomatis (nvCT) containing a 377 bp deletion in cryptic plasmid was reported in Sweden in late 2006. nvCT accounts for about 10 to 70% of the CT positive cases in certain counties in Sweden. The deleted region includes the CT primer binding sites for the Abbott RealTime CT/NG and CT assays.

Objective:
We have developed a modified formulation of the Abbott RealTime CT/NG and CT assays to detect nvCT. The modified formulation includes an additional set of CT primers and probe targeting a region of the cryptic plasmid outside the deletion. The performance of the modified formulation was compared to that of the original formulation and the Aptima Combo 2 (Gen-Probe) assay.

Method:
250 urine samples were collected and tested per manufacturer's instructions.

Result:
For Chlamydia trachomatis (CT), the two Abbott formulations agreed on 36/36 positives and 212/214 negatives. For Neisseria gonorrhoeae (NG), the two formulations agreed on 11/11 positives and 239/239 negatives. The performance concordance was also compared between the Abbott RealTime CT/NG assay with modified formulation and the Aptima Combo 2 assay. For CT, the two assays agreed on 37/41 positives and 208/209 negatives. There were 4 unique Gen-Probe positives and 1 unique Abbott positive. For NG, the two assays agreed on 11/11 positives and 239/239 negatives.

Conclusion:
Both the original and modified formulations of the Abbott RealTime CT/NG and CT assays provide sensitive and specific methodology for detection of CT and NG.

Implications:
A modified formulation of the Abbott RealTime CT/NG and CT assays has been developed for detection of nvCT.
(Product in development. Not available in the US.)