Vaginal swabs preferred over urine samples for chlamydia, gonorrhea testing

Key takeaways:

• Compared with urine samples, vaginal swabs had significantly greater sensitivity for chlamydia and gonorrhea.
• Barriers to performing vaginal swabs remain, including indiscreetness and physician hesitancy.

Evidence from nearly 30 studies support vaginal swabs as the optimal specimen for chlamydia and gonorrhea testing rather than urine samples, with the latter representing a “disservice” with long-term consequences, according to researchers.

Kristal J. Aaron, DrPH, MSPH, BS, a clinical data manager at the University of Alabama at Birmingham, and colleagues wrote in Annals of Family Medicine that the CDC recommends vaginal swabs as ideal testing for chlamydia, gonorrhea and trichomoniasis, but current laboratory-based screening for these sexually transmitted infections among women “often relies on urine specimens.”

Despite its prevalent use, Aaron and colleagues noted that urine testing has the lowest organism load compared with vaginal swabs and cervical swabs.

“While the CDC recommendations suggest that first-catch urine is acceptable for women, it may detect up to 10% fewer infections compared with vaginal swabs,” they wrote.

To determine the diagnostic sensitivity between the two tests, Aaron and colleagues analyzed data from 28 studies published from 1995 to 2021. Among those, 30 had comparisons for chlamydia, 16 had comparisons for gonorrhea and nine had comparisons for trichomoniasis.

The researchers reported that the pooled sensitivity for vaginal swabs was:

• 94.1% (95% CI, 93.2-94.9) for chlamydia;
• 96.5% (95% CI, 94.8-97.7) for gonorrhea; and
• 98% (95% CI, 97-98.7) for trichomoniasis.

Urine swabs were associated with a sensitivity of:

• 86.9% (95% CI, 85.6-88) for chlamydia;
• 90.7% (95% CI, 88.4-92.5) for gonorrhea; and
• 95.1% (95% CI, 93.6-96.3) for trichomoniasis.

However, the odds ratio that vaginal swabs were more sensitive than urine swabs were only statistically significant for chlamydia (OR = 2.69; 95%; 2.21-3.28) and gonorrhea (OR = 3.68; 95% CI, 2.19-6.18), not for trichomoniasis.

Aaron and colleagues wrote that a thorough assessment of patients’ sexual history is “essential” for determining the risks and benefits of vaginal swabs, as well as patients’ comfort level with them.

“Self-collected vaginal swabs may be preferred, especially for patients with a trauma history as the patient may become upset if a provider performs the procedure,” they wrote.

Ultimately, the researchers concluded they cannot continue “to justify the use of urine except for women for whom collection of a vaginal sample is not acceptable.”

In a related editorial, Sarah M. Wood, MD, MSHP, an assistant professor of pediatrics at the Children’s Hospital of Philadelphia, and Alexander G. Fiks, MD, MSCE, a professor of pediatrics at the same institution, wrote that the differences in sensitivity may seem small, but “the population health impact of this sensitivity gap is substantial” when considering the context of the rising prevalence of chlamydia and gonorrhea in the United States.

“Transitioning to vaginal, rather than urine, specimens in our patients could have critical population health impact by increasing early treatment and reducing downstream transmission,” they wrote.

However, Wood and Fiks highlighted several barriers to vaginal sampling, such as its indiscreetness, the possibility of alienating patients or families “without sufficient discussion,” and hesitancy from physicians to change their STI testing patterns.

Moving forward, Wood and Fiks wrote that it will be important to understand how to convince providers to use vaginal swabs. However, “placing the onus of change on clinicians alone will be insufficient to move the needle,” they wrote.

“Improvement frameworks must also engage adolescents in youth-centered research to explore message framing to maximize acceptability of a more invasive and sensitive sampling type in primary care settings,” they wrote. “We also need to consider parents and guardians as stakeholders, as parental involvement in sexual health discussions, when acceptable to adolescents, can improve sexual health outcomes.”

References:

• Aaron K, et al. Ann Intern Med. 2023;doi:10.1370/afm.2942.
• Database analysis of commercially available STI tests supports vaginal swabs as most reliable detection method. https://www.eurekalert.org/news-releases/984192. Accessed March 30, 2023. Published March 28, 2023.
• Wood S, Fiks A. Ann Intern Med. 2023;doi:10.1370/afm.2959