Literature review > Issue 1 > Review Whiley et al. 

PCR has proven to be a highly sensitive and specific method for the diagnosis of N. gonorrhoeae infections, with the advantage of using non-invasive samples such as urine. Real-time PCR assays offer an additional advantage of rapid turn-around time for results. The authors compared a LightCycler PCR (LC-PCR) with an "in-house" PCR to examine 152 urine specimens for the presence of N. gonorrhoeae DNA, to determine the clinical application of such a technique. While this is a worthwhile goal, there are some issues regarding this study that should be pointed out:

1. The use of convenience samples: It would have been helpful for the interpretation of the data to know how the specimens were selected. The article didn't tell us where the participants came from, how the urine samples were collected, stored, and transported to the laboratory, or where the study took place. It is of importance to give the background information of tested population, i.e., the incidence of the disease and if they are symptomatic or not, when a diagnostic test is evaluated. Previous studies have shown that PCR essays are less sensitive for urine specimens from women compared to those from men.

2. Discrepant results between the two tests: There were two specimens that were positive by the "in house" PCR-ELAHA and negative by the LC-PCR assay. It would be better to confirm those two specimens with another test. The author claimed that the two specimens were from asymptomatic subjects (but we still didn't know whether they were male or female), and that the majority of subjects presenting to their hospital were from symptomatic cases. They also stated in the results section that their in-house PCR is 10 times more sensitive than the LC-PCR. So to clarify if these specimens were really negative (i.e. the in-house PCR was giving a non-specific false positive result) or they were false-negative because of the lower sensitivity of the LC-PCR, the authors should have compared the LC-PCR with a well accepted "gold standard" assay in addition to an "in house" test.

3. Quantitation: the LC-PCR is designed as a quantitative method. It is disappointing that the authors did not give a lower detection limit for the 2 assays described in terms of bacterial count. The sources of tested strains, including N. gonorrhoeae and other strains for specificity tests, should be described. The detection limit of the LC-PCR the authors described was just a dilution of 10-5 of genomic DNA extracted from a single colony.

4. Specificity of both PCR assays: The target for both PCR assays in this study is the cppB gene of N. gonorrhoeae. A recent study comparing the specificity of different nucleic acid amplification assays used for the detection of N. gonorrhoeae found that assays based on the cppB gene suffer from potentially false-positive results due to cross-reactivity with Neisseria cineria and false-negative results due to the inability to detect isolates with the PA0U auxotype (Palmer HM et al. Evaluation of the specificities of five DNA amplification methods for the detection of Neisseria gonorrhoeae. J Clin Microbiol 41:835-7, 2003).

A larger study to evaluate the performance of the assay among different populations with various infection rates, or, analysis of the results based on stratification of the specimens into male or female groups would be informative.

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