Vaginal Microorganism Lactobacillus iners Linked with Chlamydia Risk

Chlamydia is the most common sexually transmitted disease in the United States, disproportionately affecting young women. Although anyone who engages in unprotected vaginal, oral, or anal sex is at risk of contracting chlamydia and other sexually transmitted infections (STIs), another factor comes into play for women: the vaginal microbiota. In fact, recent research has revealed that the composition of a woman’s vaginal microbial makeup—specifically, a preponderance of the bacteria Lactobacillus iners (L. iners)—may mean she’s more likely to be infected with Chlamydia trachomatis (C. trachomatis).

Dutch researchers carried out a study of 115 women who had participated in an earlier chlamydia screening. Of these women, 60 were found to have contracted chlamydia within a year of the baseline screening and 55 were free of chlamydia at the one-year mark; the latter served as controls. After analyzing the composition of the women’s vaginal microbiota and accounting for other variables, the researchers found that those dominated by L. iners were positively associated with the acquisition of chlamydia. The study also found a correlation between chlamydia contraction and involvement in a relationship with someone with whom the subject was not living, possibly due to casual sexual relationships outside of the primary one. The participants were mostly Dutch Caucasian women whose average age was 23 and who were deemed at low risk for sexually transmitted infections.

Prior research seems to support the idea that lactobacilli generally are protective against disease, but the Dutch team’s findings inject a note of caution. “[Our findings] supported our hypothesis that aspects of the vaginal microbiota might create an environment associated with increased susceptibility to sexually-transmitted pathogens and that the environment either strongly favors or protects against C. trachomatis infection,” the authors wrote in their report.

Women’s vaginal microbiota can vary due to a multitude of factors, according to the researchers. “We know that various factors like diet, antibiotic use, vaginal douching, menstrual cycle, having sex, etc., can alter the composition of the vaginal microbiota,” Robin van Houdt, PhD, a clinical molecular biologist at VU University Medical Center in Amsterdam and the lead author of the study, told Contagion^®. “We are not sure why certain women in our study have vaginal microbiota dominated by L. iners. What we do know from a previous study is that vaginal microbiota dominated by L. iners has been shown to exhibit a rapid change in composition in and out of community states similar to those observed in bacterial vaginosis (BV). This BV-state microbiota has also previously been demonstrated to be linked to acquiring STIs.”

At this point in time, there are no specific recommendations for sexually-active women regarding vaginal microbiota and chlamydia risk other than to practice safe sex. “Research on vaginal microbiota as a risk factor for STIs is still an emerging field and direct translation to clinical practice is not clear yet,” Charlotte van der veer, MSc, a PhD student at the Public Health Laboratory of Amsterdam and a researcher who has worked on similar studies, told Contagion^®. “Prevention strategies for STIs are still first and foremost directed at behavioral and biomedical interventions such as condoms and pre-exposure prophylaxis use, as in the case of preventing HIV infection.”

Laurie Saloman, MS, is a health writer with more than 20 years of experience working for both consumer and physician-focused publications. She is a graduate of Brandeis University and the Medill School of Journalism at Northwestern University. She lives in New Jersey with her family.