New Molecular Test Aids in Diagnosing Common Causes of Vaginitis

Johns Hopkins Medicine researchers have recently reported that a new molecular-based diagnostic test is capable of accurately diagnosing the most common bacterial, fungal, and protozoan causes of vaginitis—vaginal inflammation that is responsible for millions of clinical visits each year in the United States. The test is able to distinguish between the 3 causes of infection, and has proven to be “as accurate as and more objective than” traditional laboratory tests.

“Diagnostic tests traditionally used to distinguish among the causes of vaginitis are archaic, quite subjective and time-insensitive, plus they require extensive training for those reading the results,” lead author Charlotte Gaydos, DrPH, MPH, professor of medicine and the director of the Johns Hopkins Center for the Development of Point of Care Tests for Sexually Transmitted Diseases at Johns Hopkins University School of Medicine, commented in a recent press release on the study.

The typical laboratory process for traditional diagnostic testing consists of growing cultures and conducting microscopic studies to detect infection in cells. Sometimes, researchers even have to perform a “whiff test,” which consists of smelling the samples as a means of distinguishing between possible causes of infection in order to then provide proper treatment.

Where most traditional diagnostic tests are subjective, the new test is objective, according to Dr. Gaydos. “Either the DNA of the causative agent is there or not; no gray area,” she explained.

So, how does the new test work? First, using real-time polymerase chain reaction (RT-PCR), the researchers are able to take a closer look at “large amounts of specific DNA sequences” from the common causes of vaginitis found in patient samples. Since the test is objective, the researchers will then be presented with a “positive” or “negative” result dependent on if “enough DNA is present to indicate infection.”

The study’s main objective was to assess how accurate the test would be when diagnosing infection in vaginal swabs that had been collected from 1640 women, ages spanning from 18 to 81 years, who were expressing the common tell-tale symptoms associated with vaginitis, such as burning and itching sensations. Using PCR, the researchers “amplified and tested for the DNA of Trichomonas vaginalis, 6 bacteria species, and 6 species of yeast.”

Each patient in the study provided the researchers with 4 vaginal swab samples. The researchers used 2 for traditional lab testing, 1 for the new test, and 1 for “use with a separate comparative genetic method used to validate the results for discrepancy analysis purposes.”

Once they had the samples, the researchers prepped them, and “added them to a cartridge equipped with all the reagents needed for PCR.” After that, they put the cartridge into a RT-PCR platform called the BD MAX System, which is able to “read” the DNA sequences, and report for each of the 3 causes of vaginitis. The researchers then compared the new test with other diagnostic methods—the traditional testing and the alternate genetic test.

Their findings?

Traditional methods found bacterial vaginosis prevalence in 37.3% of patients, whereas the new molecular testing method found it in 36.1% of patients; traditional methods found that 14.7% of patients tested positive for yeast infection, and the new molecular testing method found positive results in 16.2% of patients; and, the traditional testing method found trichomonas prevalence in 1.5% of patients, whereas the new molecular method found it in 1.6% of patients.

“Overall, the disease prevalence identified by the traditional and the new molecular methods were similar,” Dr. Gaydos noted. The authors concluded that the test, using vaginal swabs collected either by clinicians or patients, "can accurately diagnose most bacterial, fungal, and protozoan causes of vaginitis."

Even though the results were similiar, Dr. Gaydos added that the new test “is faster than performing separate tests for each cause of vaginitis, is more sensitive, and, unlike current tests, can detect species of bacteria that cannot be easily grown in the lab.” In addition, the molecular test can be beneficial for clinicians when they are making treatment decisions for certain patients, in that it is also capable of testing separately for 2 different species of antibiotic-resistant yeast: Candida glabrata and C. krusei.

It should be noted that the test is not without its limitations. First, the test can cost anywhere from $75 to $125—which is, admittedly, more expensive than traditional testing methods. Another limitation is that the test needs to be sent to a laboratory with PCR capabilities—this could take hours or even days, and could hinder timely diagnosis. However, despite these drawbacks, objectivity of the test results allows for an accurate and detailed diagnosis; according to the press release, this should cut back on the number of patients returning to clinics for the same illness, and thus, could save clinics a good deal of money and time.

On October 28, 2016, the US Food and Drug Administration approved market authorization for the assay to be used by diagnostic laboratories. The assay, licensed to Becton Dickinson Diagnostics, will be marketed under the BD MAX Vaginal Panel. For future research, the team hopes to further assess the test’s accuracy and to develop an even better diagnostic tool that is capable of producing timelier results.