Literature review > Issue 7 > Review on Young et al. 

This paper is closely related to a previous publication already reviewed in this web site [1]. The authors approach the usefulness of ligase chain reaction (LCR) for the diagnosis of both rectal and pharyngeal gonorrhea among homosexual men attending a Scottish clinic in comparison to the culture of Neisseria gonorrhoeae (GC) on modified NYC medium from rectal and throat swabs.

LCR detected a true prevalence of 7% (16/227), after GC pilin gene LCR discrepancy analysis, of rectal N. gonorrhoeae infection compared to 4% by culture. Accordingly, the prevalence of pharyngeal gonorrhea was 12.7% (32/251) by LCR and 6% by culture. Authors utilized the confirmatory pilin LCR only for pharyngeal or rectal culture negative/ LCR positive specimens, as an expanded "gold standard". Specificity and sensitivity of the nucleic acid amplification test (NAAT) were very high for GC infections of both specimen types that were addressed, as expected.

Even though LCR or any other NAAT is not officially validated for the diagnosis of rectal and pharyngeal gonorrhea, data collected in this study certainly add evidence that NAATs deserve consideration as a convenient alternative to diagnose non-genital GC infection in high risk populations for the acquisition and transmission of sexually transmitted diseases [1].

In regard to the specific use of LCR in this context, this will not be possible, as acknowledged by the authors, because the test was withdrawn from the market nearly a couple of years ago. Thus, validating studies with other NAATs are expected to lend definitive support to the matter posed.

It should be reminded that this technology may help gonorrhea diagnosis mainly in developed settings, as this approach is not affordable in most developing ones, where the diagnostic resource needed might be provided only by rapid testing [2]. Furthermore, it is also true that not all GC positive samples by NAAT would be infectious, because bacterial DNA may remain in the host after successful chemotherapy in the absence of viable microorganisms.

The authors recognize the limitation of their study in regard to the inability of LCR GC diagnosis to allow antimicrobial susceptibility testing. Nevertheless, it would have been interesting if they had repeated the LCR/culture after their patients were treated [3]. This point of antimicrobial treatment was not mentioned in the paper. Another important issue discussed by the authors is the asymptomatic nature of pharyngeal and rectal gonorrhoea and the convenience of a routine screening method by NAATs among men who have sex with men. However, in this paper they missed the opportunity to document the clinical situation among their own patients and to provide information, for example, about any recent treatment of their patients for gonorrhea or their HIV status (it is also mentioned that chlamydia and syphilis screening were performed, but the results were not presented).

Finally, it is worth considering that NAAT diagnosis of gonorrhea may prove in time to be useful to identify and treat non-genital gonococcal infection in the general population.

References:

1. Page.-Shafer K, Graves A, Kent C, Balls JE, Zapitz VM, Klausner JD. Increased sensitivity of DNA amplification testing for the detection of pharyngeal gonorrhea in men who have sex with men. Clin Infect Dis. 2002; 34: 173-176.

2. Mabey D, Peeling RW, Perkins MD. Rapid and simple point of care diagnostics for STIs (Editorial). Sex Transm Infect. 2001; 77: 397-401.

3. Bachmann LH, Desmond RA, Stephens J, Hughes A, Hook III EW. Duration of persistence of gonococcal DNA detected by ligase chain reaction in men and women following recommended therapy for uncomplicated gonorrhea. J Clin Microbiol. 2002; 40: 3596-3601.

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