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Background: Nucleic acid amplification tests (NAATs) are not FDA-cleared for diagnostic testing of chlamydial (CT) or gonococcal (GC) infection in extragenital sites. In men who have sex with men (MSM), CT and GC infections of the oropharynx (ORO) or rectum (REC) may be common. There have been some concerns about false-positive NAAT results from these sites.
Objectives: To evaluate the specificity of APTIMA Combo2 (AC2, Gen-Probe Inc.) and ProbeTec (SDA, Becton Dickinson, Co.) on these specimens.
Methods: AC2 and SDA were performed on ORO and REC swabs from 1110 MSM seen in a STD clinic. NAAT positive specimens were retested by AC2, SDA and by either APTIMA CT Assay (ACT), or APTIMA GC Assay (AGC) which target rRNA sequences different from AC2.
Results:Only 11 ORO CT infections were detected. SDA detected CT in 43 REC specimens, and GC in 69 ORO and 70 REC. The three test confirmation was 100%, 94% and 99%. The AC2 detected CT in 67 REC specimens, and GC in 81 ORO and 85 REC specimens. Respective total confirmation was 94%, 91% and 94%. SDA only confirmed 71.2% (166/233) of these AC2 positives, but AC2 confirmed 91.2% (166/182) of the SDA positives. Both AC2 and SDA had high specificities (≥99.6%).
Conclusions:In our MSM population, positive results obtained with AC2 and SDA are reliable, with PPVs >90%. The CT and GC NAAT positives were confirmed to a high degree. As expected, repeat testing, or using the ACT or AGC test, confirm more of the AC2 positive results than did the less sensitive SDA.
Implications for Programs, Policy, and/or Research: In some populations, such as ours, false positive NAAT results are uncommon, and confirmatory testing is not needed. NAAT manufacturers should seek FDA-clearance for ORO and REC specimens. For now, laboratories must validate NAATs for use on extragenital sites.