Literature review > Issue_3 > Review Schwebke et al. 

The study by Schwebke and Lawing addresses the need for Trichomonas vaginalis detection methods that are more sensitive than culture. This report describes the performance of PCR for detecting T. vaginalis in 300 men attending an STD clinic in the southeastern United States. The selection of participants is clearly described and appropriate. The methods are sound and generally well-described, but there are a few inconsistencies and missing details that might make performance of the tests difficult to replicate. For instance, two urethral swabs were reportedly collected into TV InPouch culture medium, but the one used for PCR is later described as being resuspended in sterile water before DNA extraction. Also, primers TV3 and TV7 were originally called TVK3 and TVK7 by Kengne et al. Several T. vaginalis PCR assays have been recently described and were cited by the authors in the introduction to this paper. In comparisons of assays used in different studies, methodological details may be critical.

The data are presented in a single table and are organized to facilitate calculations of sensitivity and specificity of individual specimen-test combinations using a combined standard of positive urethral swab or urine culture for comparison. The number of subjects is relatively small, resulting in wide confidence intervals for test sensitivity estimates. The authors are to be applauded for having avoided the pitfall of discrepant analysis that can result in overestimates of PCR specificity. However, only samples that were culture positive, PCR negative appear to have been retested to determine if PCR inhibitors were present.

The discussion focuses on the need for better trichomonas diagnostics in general and in men in particular. For trichomonas detection in men, many details of the test including primer selection, the choice of specimen and preparation techniques can profoundly influence calculations of sensitivity and specificity. By including two specimens, urine and urethral swabs, in both the PCR diagnostic test and the culture standard, Schwebke and Lawing improved the design of the current study compared to our earlier work based on urethral swab detection only. A discussion of the impact of this fundamental difference in study design might have been more informative than focusing on the apparently greater sensitivity of one test over the other.

There seems little doubt that nucleic acid amplification detection assays for T. vaginalis infection in men and women represent an improvement over culture, just as they have been for gonorrhea and chlamydia detection. In the short term, estimates of the prevalence of trichomoniasis in different populations will improve as studies are designed using this technology. Whether development of these assays results in improved screening and treatment for T. vaginalis infections remains to be seen.

about SDI | newsletters | grants | publications | literature reviews

WHO Home - WHO Search - TDR Home - SDI Home - SDI Contact us
(c) WHO/OMS 2001