Literature review > Issue_2 > Review Garrow et al. 

It has become obvious over the last few years that screening for sexually transmitted infections should also be performed in settings in addition to specialist clinics where patients have sort care and are predominantly symptomatic. Screening in primary care settings, some of which may be in remote areas, such as in this paper by Garrow et al. requires a specimen that can be collected in a manner acceptable to the patient who has attended for many reasons other than screening for STIs. It is also essential that the test used has a high specificity to avoid high numbers of false positives in low prevalence populations.

Garrow et al. have compared the performance of self-obtained low vaginal swabs (SOLVS) with a first void urine (FVU) and with specimens taken by clinical examination, an endocervical swab (ECS) and a low vaginal swab (LVS). The women taking part in the study were from remote parts of Western Australia although there is no indication in the paper of the number of clinical sites that participated. The design of the study addresses two questions, how good are self-taken specimens for diagnosis of gonorrhoea, chlamydial infection and trichomoniasis, and can self-taken swabs be used in remote areas. The combination of the two questions may have influenced the results as the study involves many clinicians, some of whom may have been less experienced (as stated by the authors), and hence collection of the specimens taken at clinical examination may not have been optimal. The strength of this approach is that the study addresses an important question in a difficult, but real life situation.

All infections were screened by nucleic acid amplification assays (NAATs) using mostly an in-house nested multiplex PCR. Unfortunately, no data or reference are given to any previous validation of this multiplex PCR by this group, which may be a particular concern, as primers directed at the gonococcal cryptic plasmid were used as the primary screen for gonorrhoea and this plasmid is known to be absent in some strains. All positives were confirmed and only specimens positive in all tests for each organism were considered true positives. It would seem probable that with stringent criteria for a positive that the results shown reflect actual infection, but the true prevalence of either gonorrhoea or chlamydia may have been higher if the sensitivity of the initial multiplex or confirmatory PCRs was not optimal. It would also have been interesting to know how many results were discrepant.

Garrow et al. have found, as have others, that nucleic acid amplification assays are a sensitive and specific method for diagnosis of gonorrhoea using non-invasive samples [1,2] and that self-taken vaginal swabs compare well with other specimens for the detection of Neisseria gonorrhoea, Chlamydia trachomatis and Trichomonas vaginalis using a combination of in-house PCRs. This study compares with a similar study by Knox et al. [3], who also compared self-collected samples to practitioner-collected samples in a remote area for the detection of N. gonorrhoeae and Chlamydia trachomatis. These studies differ in that Knox et al. used the commercially available COBAS-AMPLICOR for the detection of N. gonorrhoeae and found that this was unsatisfactory if used alone and a confirmatory test was essential. Garrow et al. used confirmatory PCRs with different targets to confirm samples positive with the first-line PCR.

Both studies found that self-taken specimens, SOLVS (Garrow et al.) and tampons (Knox et al.) were suitable and acceptable specimens for screening for STIs in remote areas and were preferable to urine. These findings have important implications for workers in many parts of the world where screening for STIs is needed and practitioner-taken samples are not acceptable to the population or in some cases chaperoning may be a problem

References:

1. Stary A., Ching S-F, Teodorowicz L, Lee H. Cpmarison of ligase chain reaction and culture for detection of Neisseria gonorrhoeae in genital and extragenitial specimens. J Clin Microbiol. 1997;35:239-242

2. Akduman D, Ehret JM, Messina K, Ragsdale S, Judson FN. Evaluation of a strand displacement amplification assay (BD ProbTec-SDA) for detection of Neisseria gonorrhoeae in urine specimens. J Clin Microbiol. 2002;40:281-283

3. Knox J, Tabrizi SN, Miller P, Law M, Chen S, Garland SM. Evaluation of self-collected samples in to practitioner-collected samples for detection of Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis by polymerase chain reaction among women living in remote areas. Sex Transm Dis 2002;29:647-54

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