Literature review > Issue_1 > Review Opaneye et al. 

Nucleic acid amplification (NAA) methods for the diagnosis of genital chlamydial infections have been shown to perform with a higher sensitivity and specificity when compared to other already well established diagnostic techniques such as culture or antigen detection methods. The performance characteristics of non-amplification methods are broadly varying when compared to NAA assays with sensitivities between 30 to 80% depending on the methodology, the detection kit, the experience of the laboratory, and the patients´ symptomatic status influencing the number of microorganisms in the specimen. Due to the high sensitivity of DNA or RNA amplification technology, noninvasive sample types such as vulvovaginal specimens in women and urine in both men and women can be used for the detection of genital chlamydial infections. This is especially important for the performance of screening programs for Chlamydia trachomatis in asymptomatic individuals. Concerning the performance of screening tests for men, noninvasive testing is the only successful strategy for chlamydia diagnosis in asymptomatic individuals.

The present study by Opaneya et al. compares an enzyme immunoassay (EIA, Abbott IMX) using urethral swabs with the ProbeTec assay by Becton Dickinson, a strand displacement amplification (SDA) assay using urine for the detection of genital chlamydial infections in men. From a total number of 61 symptomatic and asymptomatic men, urethral specimens were tested by the EIA and urine specimens by the ProbeTec assay including an inhibition control for each sample. According to general recommendations, positive results of the EIA were confirmed by either a blocking reaction or immunofluorescence antibody test. Out of the 61 individuals, samples of 7 men (11.5%) tested positive for C. trachomatis by either assay: 2 by EIA only, 3 by SDA only, and 2 by both assays. The authors postulate that both methods were effective, although the SDA showed some superiority to the antigen detection method.

Some comments regarding the study design and evaluation are important to be pointed out.
The number of 61 individuals included in this evaluation study during a period of 5 months is low. Even lower is therefore the number of men with and without symptoms, both included in the study. Although the authors calculated 11.5% of men to be infected with Chlamydia trachomatis, the total number of 7 infected individuals does not allow a serious calculation of sensitivities and specificities. In terms of analysis, the authors did not include information on the evaluation of discrepant results between both methods in order to define a true positive result. Thus a result positive in the EIA or SDA but negative in the other method was not further evaluated by any other technique or by a second NAA assay but was considered to be true positive. To establish the true number of infected individuals it would have been important to perform a second NAA assay on all urine samples.

The sensitivity resulting from this analysis was 50% for the SDA and therefore very low when compared with data in the literature. Although it might be expected that the SDA would be positive in all EIA positive persons, the lack of further analytic procedures and the low number of infected individuals does not allow any further conclusions.

In summary, this study has been performed in a small number of male individuals for getting a first insight in the use of the ProbeTec according to the local circumstances of chlamydia testing, but does not allow any further conclusions on the characteristics of the assay in this small group of symptomatic and asymptomatic men.      

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