Spotting STIs: Vaginal Swabs Work Best

Vaginal swabs are more effective than urine analysis in detecting certain types of sexually transmitted infections (STIs), researchers have found.

In the study, which was published online March 27 in the Annals of Family Medicine, investigators found that the diagnostic sensitivity of commercially available vaginal swabs was significantly greater than that of urine tests in detecting certain infections, including those caused by Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis.

Researchers studied chlamydia and gonorrhea, which are two of the most frequently reported STIs in the United States. Trichomoniasis is the most curable nonviral STI globally, with 156 million cases worldwide in 2016.

The Centers for Disease Control and Prevention (CDC) has long recommended that vaginal swabs be used to produce optimal samples.

But despite the CDC’s recommendation, urine analysis for these STIs is more commonly used than vaginal swabs among US healthcare providers.

“We’re using a poor sample type, and we can do better,” said Barbara Van Der Pol, PhD, a professor of medicine and public health at the University of Alabama at Birmingham and an author of the new study, a meta-analysis of 97 studies published between 1995 and 2021.

Vaginal swabs for chlamydia trachomatis had a diagnostic sensitivity of 94.1% (95% CI, 93.2% to 94.9%; P < .001), higher than urine testing (86.9%; 95% CI, 85.6% to 88.0%; P < .001). The pooled sensitivity estimates for Neisseria gonorrhoeae were 96.5% (95% CI, 94.8% to 97.7%; P < .001) for vaginal swabs and 90.7% (95% CI, 88.4% to 92.5%; P < .001) for urine specimens.

The difference in pooled sensitivity estimates between vaginal swabs and urine analyses for Trichomonas vaginalis was 98% (95% CI, 97.0% to 98.7%; P < .001) for vaginal swabs and 95.1% (95% CI, 93.6% to 96.3%) for urine specimens.

STIs included in the study are not typically found in the urethra and appear in urine analyses only if cervical or vaginal cells have dripped into a urine sample. Van Der Pol and her colleagues estimated that the use of urine samples rather than vaginal swabs may result in more than 400,000 undiagnosed infections annually.

Undiagnosed and untreated STIs can lead to transmissions of the infection as well as infertility and can have negative effects on romantic relationships, according to Van Der Pol.

Sarah Wood, MD, an attending physician at Children’s Hospital of Philadelphia, said some healthcare providers may use urine analysis because patients may be more comfortable with this method. The approach also can be more convenient for medical offices: All they must do is hand a specimen container to the patient.

Conversations between clinicians and patients about vaginal swabbing may be considered “sensitive” and the swabbing more invasive, Wood, an author of an editorial accompanying the journal article, said. Clinicians may also lack awareness that the swab is a more sensitive method of detecting these STIs.

“We all want to do what’s right for our patient, but we often don’t know what’s right for the patient,” Wood said. “I don’t think people are really aware of a potential real difference in outcomes with one method over the other.”

Wood advised making STI screening using vaginal swabs more common by “offering universal opt-out screening, so not waiting until you find out if someone’s having sex but just sort of saying, ‘Hey, across our practice, we screen everybody for chlamydia. Is that something that you want to do today?’ That approach sort of takes out the piece of talking about sex, talking about sexual activity.”

Van Der Pol, who said she has worked in STI diagnostics for 40 years, said she was not surprised by the results and hopes the study changes how samples are collected and used.

“I really hope that it influences practice so that we really start using vaginal swabs, because it gives us better diagnostics for chlamydia and gonorrhea,” Van Der Pol said.

“Also, then starting to think about comprehensive women’s care in such a way that they actually order other tests on that same sample if a woman is presenting with complaints.”

Ann Fam Med. Published online March 27, 2023. Full text, Editorial

Robert Fulton is a journalist located in Los Angeles.

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