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DNA amplification test offer the most specific and sensitive test to date. In particular, their ability to be performed on first-catch urine rather then swab specimens has dramatically expanded options for screening in prevention programs, particularly the targeting of asymptomatically infected males. Their advantages also include the ability to detect as little as a single gene copy*. This improves their ability to screen for infections in low prevalence and asymptomatic populations. The fact that these test do not depend on intact or viable organisms for positive results may be one of the explanations for discrepancy between culture and amplification test. Other advantages of NAAT is that turn around time for results is much shorter then compared to culture; most can be performed in 4-5 hours with results available within 24 hours. For several of the assays, one specimen can be used for detection of both Chlamydia and Gonorrhea. There was initial concern about false positive results due to contamination or splash-over between specimens, but these are less of a problem than false negatives and can be corrected by improved laboratory procedures. PCR became commercially available in 1993 and has been widely evaluated in endocervical, male urethral, and male and female urine specimens. The test is based on a polymerase chain reaction (PCR), which produces a logarithmic amplification of a target 207 pair cryptic plasmid DNA sequence. The PCR products, or amplicons, are detected using an oligonucleotide capture probe and a substrate to produce a colorimetric reaction that can be read by a spectrophotometer. Comparison of Sensitivity and Specificity of PCR and LCR in Different Specimens
(* Livengood, C.H., 3rd, etal., Performance of a commercial polymerase chain reaction test for endocervical Chlamydia trachomatis infection in a university hospital population. Infectious Disease in Obstetrics and Gynecology, 1998. 6(5): p.224-9) NAAT is the most applicable technology for screening in low prevalence populations and can be performed with non-invasive sampling. Its sensitivity is the highest, thereby missing the smallest proportion of infections. Specificity is also extremely high, resulting in a high positive predictive value. Because a majority of genitourinary Chlamydia infections are asymptomatic and occur in relatively low prevalence populations, NAAT is one of the best solutions for widespread detection and treatment of infections. |