Vaginal swabs better at spotting STIs than urinalysis

 Contrary to practice, vaginal swabs are more effective than urine analysis in detecting certain types of sexually transmitted infections (STIs) as shown in a meta-analysis.

 

The diagnostic sensitivity of commercially available vaginal swabs was significantly greater than that of urine tests in detecting infections caused by Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis. [Ann Fam Med 2023; 21:172-179]

The US Centers for Disease Control and Prevention (CDC) recommends vaginal swabs to produce optimal specimens. But despite the guidance, urine analysis is more widely used than vaginal swabs in detecting STIs.

“We’re using a poor sample type, and we can do better,” said study author Professor Barbara Van Der Pol from the University of Alabama at Birmingham, Alabama, US. She was not surprised by the results and hopes the study changes how samples are collected and used globally.

 

Her team identified 28 eligible articles with 30 comparisons for C. trachomatis, 16 comparisons for N. gonorrhoeae, and 9 comparisons for T. vaginalis.

 

Vaginal swabs for C. trachomatis had a diagnostic sensitivity of 94.1 percent (p<0.001) relative to 86.9 percent for urine testing (p<0.001).

 

The pooled sensitivity estimates for N. gonorrhoeae were 96.5 percent (p<0.001) for vaginal swabs and 90.7 percent (p<0.001) for urine specimens.

 

The difference in pooled sensitivity estimates between vaginal swabs and urine analyses for T. vaginalis was 98 percent for vaginal swabs and 95.1 percent for urine specimens (all p<0.001).

 

STIs included in the study are not typically found in the urethra and appear in urine analyses only if cervical or vaginal cells are dripped into a urine sample. Van Der Pol said continued urine sampling could lead to more than 400,000 missed cases of chlamydia and gonorrhea annually.

 

Undiagnosed and untreated STIs can lead to infection transmissions and infertility and can have negative effects on romantic relationships, she added.

In an accompanying editorial, Dr Sarah Wood from the Children’s Hospital of Philadelphia said patients find urinalysis more comfortable than vaginal swabbing and is more convenient for diagnostic units. “You just need to hand in a specimen container to the patient and all’s done in minutes.” [Ann Fam Med 2023;21:100-102]

Additionally, conversations between clinicians and women about vaginal swabbing may be considered “sensitive” and the swabbing “more invasive,” she continued. “Not all clinicians may be aware that vaginal swab is more sensitive in detecting these STIs.”

 

“We all want to do what is right for our patients, but we often do not know what’s right for them,” Wood said. “I don’t think most clinicians are aware of the potential real difference in outcomes with one approach over the other.”

“As clinicians caring for our patients, we interpret these findings as necessitating a shift in practice. Transitioning to vaginal, rather than urine, specimens in our patients could have critical population health impact by increasing early treatment and reducing downstream STI transmission,” Wood added.