Abstract
Sirs: We read with great interest the important paper by Falk et al. 1 regarding sampling for Chlamydia trachomatis (CT) infection. The authors conclude that the sensitivity of self-collected vaginal swabs (SCVS) is as high as that of combined vaginal/first catch urine (FCU) specimens. The study highlights an important topic as CT is a very common infection, and several tests are taken every year to quite a high cost. The authors, however, refer to two different diagnostic methods for detecting CT, polymerase chain reaction (PCR) by Roche and strand displacement amplification by Becton, Dickinson and Company (B&D), methods that are not completely comparable.
One study from the Netherlands 1 regarding 50 CT-positive women shows that combined SCVS and FCU sampling detects 50/50 CT-positive women, while SCVS detects 48/50. In the study by Falk et al. 1 63 CT-positive women were detected by the B&D test, 60/63 by SVCS and 61/63 by combined SVCS and FCU.
These two studies, including the one by Falk et al. 1,2 indicate that SCVS combined with FCU may be the sampling method of choice when using the B&D test, whereas when using PCR by Roche the same studies indicate that SCVS is at least as good as the combination of SCVS/FCU and that FCU does not increase the sensitivity. These results are applicable when gynaecological examination and sampling from cervix is not done as this method might be somewhat more sensitive. 1
As these studies are quite small, we therefore emphasize the need for further, larger studies regarding optimal sampling methods when using common commercially available diagnostic methods, as well as the necessity of investigating differences between methods for diagnosing genital CT infections in women.