Endocervical samples, cultures have lower detection rates
In this study, endocervical samples collected by the clinician 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 five gonorrhea infections (in women with and without symptoms).
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 at 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 practice providers 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 clinician-collected NAAT testing.
1. Schoeman SA, Stewart CM, Booth RA, et al. Assessment of best single sample for finding chlamydia in women with and without symptoms: a diagnostic test study. BMJ. 2012;345:e8013.
2. Stewart CM, Schoeman SA, Booth RA, et al. Assessment of self taken swabs versus clinician taken swab for cultures for diagnosing gonorrhea in women: single centre, diagnostic accuracy study. BMJ. 2012;345: e8107.
3. CDC. Fact sheet: STD trends in the United States—2011 national data for chlamydia, gonorrhea, and syphilis (2012). www.cdc.gov/std/stats11/trends-2011.pdf. Accessed November 15, 2013.
4. CDC. Fact sheet: Incidence, prevalence, and cost of sexually transmitted infections in the United States (2013). www.cdc.gov/std/stats/STI-Estimates-Fact-Sheet-Feb-2013.pdf. Accessed November 15, 2013.
5. United States Preventive Services Task Force. USPSTF Recommendations for STI screening (2008). www.uspreventiveservicestaskforce.org/uspstf08/methods/stinfections.htm. Accessed November 15, 2013.
6. CDC. 2010 STD treatment guidelines. www.cdc.gov/std/treatment/2010/default.htm. Accessed November 15, 2013.
7. Cook RL, Hutchison SL, Østergaard L, et al. Systematic review: non-invasive testing for Chlamydia trachomatis and Neisseria gonorrhoeae. Ann Intern Med. 2005;142:914-925.
8. Moss S, Mallinson H. The contribution of APTIMA Combo 2 assay to the diagnosis of gonorrhoea in genitourinary medicine setting. Int J STD AIDS. 2007;18:551-554.
9. Chernesky MA, Hook EW 3rd, Martin DH, et al. Women find it easy and prefer to collect their own vaginal swabs to diagnose Chlamydia trachomatis or Neisseria gonorrhaea infections. Sex Transm Dis. 2005;32: 729-733.
The PURLs Surveillance System is supported in part by Grant Number UL 1RR 024999 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.
Copyright © 2013. The Family Physicians Inquiries Network. All rights reserved.
Reprinted with permission from the Family Physicians Inquiries Network and The Journal of Family Practice. 2013;62(11):651-653.