Characterizing the bacterial surface profiles of menstrual cups and their association with user characteristics and vaginal microbiomes in an adolescent cohort from western Kenya

Background Menstrual cups are increasingly promoted in low-resource settings as long-lasting and cost-effective menstrual hygiene solutions. However, no studies have been done among cup users to characterize the bacterial communities found on cups with long-term use when stored. This study sought to comprehensively characterize the bacterial surface profile of the menstrual cup, identify factors associated with putative pathogens, and quantify the vaginal microbiome as potential source for menstrual cup bacterial communities. Methods Over 30 months of follow-up, 369 menstrual cup samples were collected from 172 secondary schoolgirls participating in a randomized controlled trial in western Kenya. Samples were obtained from cups brought to school by girls during study visits. Menstrual cup and vaginal microbiomes were assessed using 16S rRNA gene amplicon sequencing. Mixed effects models were applied to identify factors associated with putative pathogens ( Escherichia coli , Staphylococcus aureus , coliform bacteria), and factors associated with vaginal microbiome as potential source environment to bacterial surface profile of the menstrual cup, estimated via fast expectation-maximization for microbial source tracking (FEAST). Results Menstrual cup bacterial surface profile composition was primarily comprised of soil and water bacteria. However, taxa specific to the vaginal microbiome (e.g., Lactobacillus crispatus , L. iners , and Gardnerella vaginalis ) were also recovered from cups. The mean relative abundance (presence) of E. coli and S. aureus was 0.09% (36%) and 0.36% (24%), respectively, with higher relative abundance among participants with HSV-2 or non-optimal vaginal community state type 4. Damaged cups were also associated with higher relative abundance of putative pathogens, while antibiotic use was inversely associated with E. coli. On average, 25.1% of cup microbiota originated from the vagina, with lower contributions among older participants and those with damaged cups. No serious adverse events related to the menstrual cup were observed in the cohort. Conclusions Interventions focused on improved cleaning and storage tools and methods, and access to clean water and sanitation infrastructure are required to maximize safety of menstrual cup use in low-resource settings.