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Enhanced Enzyme Immunoassay with Negative-Gray-Zone Testing Compared to a Single Nucleic Acid Amplification Technique for Community-Based Chlamydial Screening of Men

Paddy Horner,^1,2* Sue Skidmore,³ Alan Herring,^4, Jo Sell,⁵ Ian Paul,⁵ Owen Caul,^4, Matthias Egger,⁶ Anne McCarthy,⁶ Emma Sanford,⁶ Chris Salisbury,⁷ John MacLeod,⁸ Jonathan Sterne,⁶ Nicola Low,⁶ for the Chlamydia Screening Studies (ClaSS) Group

The Milne Centre, United Bristol Healthcare NHS Trust, Bristol BS2 8HW,¹ Department of Pathology and Microbiology, University of Bristol, Bristol,² Royal Shrewsbury Hospital Trust, Shrewsbury,³ Public Health Laboratory Service Bristol Laboratory, Bristol BS2 8EL,⁴ Health Protection Agency, Myrtle Road, Bristol BS2 8EL,⁵ Department of Social Medicine, University of Bristol, Bristol BS8 2PR,⁶ Division of Primary Care, University of Bristol, Bristol BS6 6JL,⁷ Department of Primary Care, University of Birmingham, Birmingham B15 2TT, United Kingdom⁸

Received 12 June 2004/ Returned for modification 28 August 2004/ Accepted 20 December 2004

We evaluated a low-cost diagnostic strategy for detecting Chlamydia trachomatis in a low-prevalence population. We used an amplified enzyme immunoassay (EIA) with a reduced-cutoff "negative gray zone" to identify reactive specimens for confirmation by a nucleic acid amplification test. As part of the Chlamydia Screening Studies project, men provided a first-pass urine specimen, which they returned by post for testing. We tested 1,003 specimens by IDEIA PCE EIA (Dako) and Cobas PCR (Roche). There were 32 (3.2%) true positive specimens according to a combined standard using an algorithm requiring concordant results from at least two independent tests. All of these were positive by Cobas PCR and 24 were confirmed to be positive by PCE EIA, including 2 that gave results in the negative gray zone. There were 971 true negative specimens, 2 of which were positive by Cobas PCR and 19 of which were initially inhibitory for PCR. The relative sensitivity, specificity, positive predictive value, and negative predictive value of PCE EIA with PCR confirmation were 75.0% (95% confidence interval [CI], 56.6 to 88.5%), 100% (95% CI, 99.7 to 100%), 100% (95% CI, 88.3 to 100%), and 99.2% (95% CI, 98.4 to 99.6%), respectively. The corresponding values for Cobas PCR were 100% (95% CI, 89.1 to 100%), 99.8% (95% CI, 99.3 to 100%), 94.1% (95% CI, 76.9 to 98.2%), and 100% (95% CI, 99.6 to 100%), respectively, with 1.9% (19/1003) of the samples being initially indeterminate. When the prevalence of C. trachomatis is low, the use of an amplified EIA on urine specimens, with confirmation of results in the negative gray zone by use of a nucleic acid amplification technique, is not suitable for screening asymptomatic men. In addition, positive nucleic acid amplification test results should be confirmed and an inhibition control should be used.

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• Skidmore, S., Horner, P., Herring, A., Sell, J., Paul, I., Thomas, J., Caul, E. O., Egger, M., McCarthy, A., Sanford, E., Salisbury, C., Macleod, J., Sterne, J. A. C., Low, N., for the Chlamydia Screening Studies (ClaSS) Projec, (2006). Vulvovaginal-Swab or First-Catch Urine Specimen To Detect Chlamydia trachomatis in Women in a Community Setting?. J. Clin. Microbiol. 44: 4389-4394 [Abstract] [Full Text]