ABOVE: A menstrual pad embedded with L-proline β-naphthylamide, which turned pink after exposure to Candida albicans

A thread laced into a tampon or pad can detect Candida albicans overgrowth—also known as a yeast infection—within 10 minutes, scientists reported in ACS Omega in May. If the product is shown to work in at-home settings, the authors say, it might allow women all over the world to quickly and inexpensively self-diagnose yeast infections, improving care—especially in resource-limited settings.

Currently, to confirm a yeast infection diagnosis, a woman has to see her doctor, have her vagina swabbed, and then wait 24–72 hours for the results of a PCR test. This is inconvenient for most women, and extremely challenging for those with limited access to health care.

A diagnosis isn’t necessary for women to purchase antifungal treatments over-the-counter, so if they experience itching or other symptoms, they can assume they have...

“Many women with these symptoms do not have yeast infections and unnecessarily use over-the-counter yeast infection medications. This diagnostic could potentially reduce the unnecessary use of yeast medications in the absence of yeast infections,” says Christine Metz, who studies molecular medicine at the Feinstein Institutes for Medical Research in New York and was not involved in the study. Using these antifungals inappropriately can delay appropriate care, waste time and money, and contribute to antifungal resistance.

The idea for the diagnostic tampon started a couple of years ago, says Naresh Kumar Mani, a biotechnologist at Manipal Institute of Technology in India and the senior author on the study. “I was discussing with my colleague—she’s an obstetrician—and also another colleague, a medical mycologist. Much emphasis is not being given to Candida albicans, though it is a disaster for immunocompromised [people], neonates, and women.” While the common symptoms are not life-threatening, Mani says, the fungus can wreak havoc if it manages to spread throughout the body. “Among ICU patients, Candida is the leading fungal pathogen causing severe sepsis or septic shock. . . . So it is crucial to detect it at early stages.” The researchers set out to create a fast and inexpensive test for self-diagnosing the infection.

First, they searched for an assay that could detect an overgrowth of C. albicans in vaginal discharge. They landed on L-proline β-naphthylamide (PRO), a substrate that reacts to L-proline aminopeptidase, an enzyme produced by C. albicans and other organisms. PRO is used in laboratory assays, and according to Mani, has existed for 30 years, but had rarely been used clinically. It is a known carcinogen.

“These substrates, the moment they contact the enzyme, it undergoes hydrolysis and results in a simple color change,” explains Mani.

Then, the researchers needed a way to make a matrix out of thread that could be embedded in a tampon or pad and carry the substrate. The researchers chose tampons and pads because they wanted to integrate their threads into products already on the market that can absorb enough of the L-proline aminopeptidase for it to be detected. Like most threads, those that the team had purchased from a local craft store had been treated with wax and hydrophobic binders that prevent them from absorbing liquids. So they washed the strings three times in a heptane solution to remove their coatings, treated them with the substrate, and threaded them into tampons and pads.

Because C. albicans ordinarily lives in the vaginal microbiome in small quantities, Mani says, the team identified the threshold at which an infection occurs and designed the assay to change color only when a high enough concentration of the enzyme is present. They exposed the treated products to simulated vaginal discharge spiked with C. albicans. When enough of the fungus was present to indicate a yeast infection, the threads turned pink. The more fungus that was present, the darker the shade of pink.

The approach needs updating before it could be used. For one, the fact that the threads turn deep pink may be an obstacle if women need to diagnose an infection while menstruating, as the indicator color could be masked by blood. Additionally, Metz points out that other pathogens, such as the bacteria Clostridium difficile, can produce the L-proline aminopeptidase enzyme.

Mani says the team is also looking for analogs to the current substrate because PRO is a known carcinogen. Another limitation is that so far, the product has only been tested with simulated samples, not on actual vaginal discharge nor in a real-world setting.

Despite these limitations, Metz says that the “low cost, simple, and rapid, at-home method for detecting vaginal yeast infections represents an advance for improving women’s health.” Mani is currently working with collaborators in the US and UK to find PRO analogs and secure funding to bring the product to market.

“Self diagnosis tools are important in increasing access [to healthcare],” says Erica Cahill, a gynecologist at Stanford University, in an email to The Scientist. “The most critical question is what will people do with tools like this? Will they be less likely to use medication when it’s negative (or will they still use it anyway based on their symptoms)? Will they be more likely to seek treatment with a positive test?”

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a white menstrual pad with pink and yellow spotting

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