Enhancing the specificity of the COBAS AMPLICOR CT/NG test for Neisseria gonorrhoeae by retesting specimens with equivocal results

B. Van Der Pol, D. H. Martin, J. Schachter, T. C. Quinn, C. A. Gaydos, R. B. Jones, K. Crotchfelt, J. Moncada, D. Jungkind, B. Turner, C. Peyton, J. F. Kelly, J. B. Weiss, M. Rosenstraus

Research output: Contribution to journalArticle

Abstract

The COBAS AMPLICOR CT/NG test for Neisseria gonorrhoeae cross-reacts with certain strains of nonpathogenic Neisseria species. In some strains, the target sequence is identical to that of N. gonorrhoeae, whereas other strains have a small number of mismatches within the regions recognized by the primers or probe used in the COBAS AMPLICOR NG test. These cross-reactive strains are occasionally present in urogenital specimens, causing false-positive results in the COBAS AMPLICOR NG test. Analysis of the data generated in a large multicenter clinical trial showed that 2.9% of the specimens gave signals between A660 of 0.2 and 3.5 but that one-half of these equivocal specimens did not contain N. gonorrhoeae. Most of these equivocal specimens were correctly classified as true positive or true negative by retesting in duplicate and defining a PCR-positive result as two of three results with an A660 of ≥ 2.0. If specimens had been classified as positive or negative based on a single test result using a cutoff of an A660 of 0.2, specificity would have ranged from 96.2 to 98.9% depending on specimen type, sex, and presence of symptoms. By employing the equivocal zone-retesting algorithm, specificity increased to 98.6 to 99.9% with little effect (0.1 to 4.9% decrease) on sensitivity in most specimen types, enabling the test to achieve a positive predictive value of at least 90% in populations with a prevalence of 4% or higher. In lower-prevalence populations, the test could be used to screen for presumptive infections that would have to be confirmed by an independent test.

Original languageEnglish (US)
Pages (from-to)3092-3098
Number of pages7
JournalJournal of clinical microbiology
Volume39
Issue number9
DOIs
StatePublished - 2001
Externally publishedYes

ASJC Scopus subject areas

  • Microbiology (medical)

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    Van Der Pol, B., Martin, D. H., Schachter, J., Quinn, T. C., Gaydos, C. A., Jones, R. B., Crotchfelt, K., Moncada, J., Jungkind, D., Turner, B., Peyton, C., Kelly, J. F., Weiss, J. B., & Rosenstraus, M. (2001). Enhancing the specificity of the COBAS AMPLICOR CT/NG test for Neisseria gonorrhoeae by retesting specimens with equivocal results. Journal of clinical microbiology, 39(9), 3092-3098. https://doi.org/10.1128/JCM.39.9.3092-3098.2001