Kayla Carter headshot with blue mountains in the background

Kayla Carter, MPH

Program: Epidemiology PhD

Hometown: Fulton, MD

Publications: View list

What was the path that led you to pursue your degree at UW Department of Epidemiology?

My undergraduate was in biology, and I did my MPH in epidemiology (epi) at the University of Michigan, and that’s when I started doing vaginal microbiome work. I had never really considered doing a PhD before then, but I was talking to my mentor about ideas for my master’s thesis and he advised that my initial idea was too much for a thesis, and suggested it could make a good dissertation, which kind of planted the seed in my mind. I really enjoyed the research and wanted to keep doing it and wanted to be the person asking the questions and writing the grants, so I figured a PhD was the right path to take.

In exploring doctoral programs, I knew I wanted to work with someone who was doing vaginal microbiome work in an epi department because I wanted more advanced and in-depth epi training. A lot of microbiome work is done in basic science or medical schools, so wanting to be in epi helped narrow down the options. Of the schools where I applied, Seattle was the place I wanted to go the most. I had the opportunity to meet Jen Balkus at Visit Days, who I knew I wanted to work with, and she had funding, so, the stars aligned for us to work together. 

Your paper on the ‘Associations between vaginal bacteria and bacterial vaginosis signs and symptoms‘ was recently published in Frontiers in Cellular and Infection Microbiology. How did the idea for this research come about? 

My central interest has been focused on vaginal microbiome research. During the first year of my PhD, I had a nagging question in the back of my mind regarding the two common ways that we evaluate bacterial vaginosis (BV). There’s Amsel criteria, which use signs and symptoms to make a clinical diagnosis, and there’s also Nugent score, which is based on Gram stain and counting different bacterial shapes on a microscope slide. There is discordance between the two measures. Typically, Nugent BV tends to be more prevalent than Amsel BV because a lot of people that are classified as having BV by Nugent score are asymptomatic and wouldn’t be classified as having BV by Amsel criteria.

I was interested in why some people with Nugent BV have symptoms and others don’t. The symptoms of BV are typically what drive people to seek treatment, and in most places, treatment isn’t recommended if someone is asymptomatic. So, I was interested in whether certain vaginal bacteria drive symptoms and by extension, care seeking and treatment. 

This paper builds on previous research with a population based in Seattle, led by Sujatha Srinivasan, who is the senior author on my paper. We thought it would be interesting to compare the results from the Seattle population to the results from a population in Kenya. There’s a bunch of evidence that BV prevalence, microbiota composition, and their associations with clinical outcomes can vary between populations. In this study, we were looking to see how generalizable or consistent the relationships between vaginal bacteria and Amsel criteria are across populations. 

What did you see in terms of the relationship between vaginal bacteria and BV symptoms? 

We observed that a group of six vaginal bacteria, BV associated bacterium 1 (BVAB1), Eggerthella type 1, Fannyhessea vaginae (formerly Atopobium vaginae), Gardnerella species, Sneathia amnii, and Sneathia sanguinegens, were associated with the presence of three to four Amsel criteria across both populations in Kenya and Seattle. So, this comparison study indicates that these six bacteria may contribute to BV symptomatology generally, regardless of population differences in vaginal microbiota composition. We also saw that a number of additional vaginal bacteria were associated with one or two Amsel criteria, so these bacteria may contribute to specific BV signs and symptoms.

How do you see these findings contributing to the understanding of BV? 

These findings give some interesting insights into BV etiology. Considering the context of prior epidemiologic and lab-based work, this study adds to the growing evidence base of the role of biogenic animes and extracellular enzymes in BV etiology. 

The microbiome field is shifting to focus more on the things that bacteria produce and how those products impact the bacterial community and the host, as opposed to focusing on the bacteria themselves. This is because different bacteria can do the same thing, different strains of the same bacteria can do different things, and lots of bacteria change their activity in response to different environmental conditions. Our study just looked at the bacteria that were present…that’s just the data we had. But considering what bacteria are present in the context of prior work about what those bacteria do, helps us get a little closer to eventually understanding the mechanisms that contribute to how BV develops, because it’s still somewhat of a mystery. 

Our findings can also contribute to the development and improved performance of molecular BV tests, which look for certain bacteria that are often present during BV to make a diagnosis. These tests aren’t very widely used yet, largely due to cost, but they may become more popular as costs continue to fall. Current molecular tests don’t look for BVAB1, Eggerthella type 1, S. amnii, or S. sanguinegens, and our results suggest that incorporating these bacteria could improve the performance of molecular BV tests, especially considering that the people who would receive these tests would likely be those presenting with signs and symptoms.

I know you’re also involved in equity, diversity, and inclusion and advocacy, how do these themes show up in your research? 

When we’re writing and reading about the vaginal microbiome and people with vaginas, it’s important to remember that not everyone with a vagina is a woman and not every woman has a vagina. Though the vast majority of the work in the area and all of my work so far is with cisgender women, I generally try to use gender-neutral terms, such as ‘individual’ or ‘participant,’ when I’m writing or presenting. I hope in the coming years, the field also moves towards using language that is more inclusive of all gender identities. That said, some researchers are doing some really exciting work with populations of trans women looking at the microbiome of the neo vagina, and with trans masculine people looking at how the genital microbiome changes with testosterone therapy. 

I appreciate the aspects of vaginal microbiome and sexual health research that contribute to advancing gender equity. Even if it’s indirectly, I hope this research supports people better understanding their bodies, being better able to make informed decisions about their bodies, and leading happier, healthier lives. 

What are your future career or research goals? 

I see myself staying in the vaginal microbiome space, which I think of as a nice union of my interests in biology, public health, and also some interesting and fun quantitative data analysis challenges. As I’ve continued working in this area, my understanding of those interesting and fun data analysis challenges has grown, and in that growth, I am finding even more complex and exciting challenges. It’s a really interesting time to be in the area, to try to move the science forward and push for rigor and reproducibility in microbiome science, particularly with an epidemiologic lens. I love it and I think it’s super interesting.