Gonorrhea: Self-collection, NAAT yield better results
Gonorrhea was found in 2.5% of the 3859 women with complete results for testing of this STI. Self-collected swabs and physician-collected swabs analyzed by NAAT both had excellent sensitivity (99% vs 96%; P=.375). But self-collected samples that underwent NAAT were significantly more sensitive than clinician-collected urethral and endocervical samples that were cultured (99% vs 81%; P<.001). The number needed to test by self-collection for NAAT (compared with clinician-collected culture) to detect one additional case of gonorrhea was 5.
In women with symptoms suggestive of infection, the NAAT assays—both physician- and self-collected—were equivalent and were more sensitive than gonorrhea culture (P=.004). In asymptomatic women, 1.8% of whom had gonorrhea, the vulvovaginal swab sent for NAAT was more sensitive than culture (98% vs 78%; P=0.008) and equivalent to the endocervical swab for NAAT (90%).
The bottom line: Self-collected vulvovaginal swabs are the sample of choice for both chlamydia and gonorrhea testing in women, regardless of whether they have symptoms. When a clinical examination is needed, either the clinician or the patient can collect a vulvovaginal swab.
WHAT'S NEW: Endocervical samples, cultures have lower detection rates
In this study, endocervical samples collected by the physician rather than self-collected vulvovaginal samples would have missed 9% (one in 11) of chlamydial infections in women with symptoms of an STI. Vulvovaginal swabs and endocervical swabs have equal sensitivity for the diagnosis of gonorrhea when NAAT is used, but culture would have missed one in 5 gonorrhea infections (in women with and without symptoms).
CAVEATS: NAAT is costly, and does not test for drug sensitivity
Although NAAT has replaced cell culture methodology as the gold standard for gonorrhea and chlamydia diagnosis, it is potentially costly if not readily available in your practice setting. What’s more, NAAT does not allow testing for antibiotic sensitivity, which is particularly relevant with increasing resistance of gonorrhea to multiple antibiotics. In addition, it’s unclear whether these results would apply to all NAAT assays or just the one used in this study.
These studies examine sensitivity and specificity of gonorrhea and chlamydia testing in a high-risk population—women who were seeking care in a sexual health center. Your patient population may be lower risk, which will lower the prevalence of STIs and lower the positive predictive value of NAAT. A positive NAAT test for an STI should be followed by a confirmation NAAT in low-risk populations.
CHALLENGES TO IMPLEMENTATION: Reconsidering the way we practice
Most family physicians are accustomed to performing a full examination on patients with a suspected STI, and changing the flow of the office visit may be difficult. And, to implement this practice changer properly, it would be necessary to provide patient instruction in self-collection technique.
Also, making this change could be costly if you do not have this particular NAAT available. Once implemented, however, self-collection with NAAT will likely save time and be more comfortable for your patients. It will also provide a higher sensitivity in detecting chlamydia infections and equal sensitivity in detecting gonorrhea compared with physician-collected NAAT testing.
ACKNOWLEDGEMENT
The PURLs surveillance system was supported in part by Grant Number UL1RR024999 from the National center for Research Resources, a clinical Translational science Award to the University of Chicago. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National center for Research Resources or the National Institutes of Health.