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Detection
of Chlamydia trachomatis by isothermal ramification
amplification method: a feasibility study.
Zhang W,
Cohenford M, Lentrichia B, Isenberg HD, Simson E, Li H, Yi J, Zhang
DY.
Journal of Clinical
Microbiology 2002;40:128-132. |
Milt Tam, PhD
Program for Appropriate Technology in Health
Seattle, WA, USA |
The past decade has seen significant advances in the development of molecular amplification technologies for detection of
Chlamydia trachomatis with the introduction of several commercial test systems. This study presented by Zhang
et al. compares the performance of their new isothermal amplification method, termed ramification amplification (RAM), with the results of a commercial molecular amplification test, the Abbott Diagnostics LCx, and a real-time PCR method performed on the Roche LightCycler.
The purpose of the study was to determine the feasibility of the RAM method for use with residual endocervical swab specimens taken and transferred to liquid medium and used for Pap staining (PreservCyt; Cytyc Corporation, Boxborough, MA). Data from only 30 selected specimens, 15 positives and 15 negatives, for which previous PCR and LCx data existed were presented. No other information was given on the origin of the specimens, how they were selected, or whether the women evaluated were symptomatic. One specimen found to be RAM-negative but PCR/LCx-positive was attributed to the lack of cellular material in the specimen. Otherwise, the data for the RAM method were concordant with the results of the other molecular tests. The analytical sensitivity of the RAM method using dilutions of cell culture-derived organisms was presented as approximately 10 elementary bodies, but there was no parallel sensitivity analysis to compare RAM to the PCR or LCx methods, or specificity analysis using
C. psittaci, C. pneumoniae, and other commensal organisms.
In summary, the RAM method seems to perform well in the laboratory using liquid specimens from endocervical swabs. It has an analytical sensitivity for
C. trachomatis in the same range as the PCR and LCx methods and is comparable in terms of its complexity, sensitivity, and the time required to produce a result. With the selected specimen panel used, there are no data yet on the performance of the RAM method on unselected specimens or from a prospective study from a family planning clinic or a largely asymptomatic population. Similarly, it will be key to evaluate other less-invasive specimens with the RAM method such as urines or self-collected vaginal swabs, since these specimens have been validated for use with other molecular amplification tests. It is unclear if the RAM method, if commercialized, will provide any distinct or significant advantages over PCR, LCx, or other nucleic acid amplification methods including Gen-Probe’s TMA, Digene’s Hybrid Capture, Becton Dickinson’s SDA, or Organon’s NASBA methods for detection of chlamydia in terms of increased speed, simplicity, dependability, accuracy, use of equipment, or lower cost
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