Lactobacillus iners-dominated vaginal microbiota was associated with increased susceptibility to Chlamydia trachomatis infection in women, in a Dutch nested case-control study.

The population base was from a large trial to investigate effectiveness of screening for chlamydia infection in the Netherlands where eligible sexually active men and women, aged 16-29 years, were offered yearly repeated chlamydia screening.

Women who tested negative for chlamydia and subsequently tested positive the following year were selected. These cases were matched, by age and ethnicity, to women who tested negative for chlamydia for two consecutive years.

The vaginal microbiota was profiled at baseline and prior to infection to evaluate changes related to chlamydia acquisition. DNA was extracted from stored vaginal swabs and sequencing was used to identify vaginal microbes.

A total of 5,458 women took part in the chlamydia screening trial, returned screening swabs at least twice and completed a questionnaire covering sexual risk behaviour and medical history. Of these women 3,503 (64%) had two yearly consecutive screenings and a negative chlamydia test at their first visit; 61 tested positive on a subsequent test and these cases were matched with 61 controls for the nested case-control study.

Information on vaginal microbiota was available for 60 of the cases and 55 controls. Five vaginal community state types (CSTs I to V) were identified; four were dominated by Lactobacillus species of which

L. crispatus (37%) and L. iners (33%) were most common. CST IV had depletion of Lactobacillus spp. and presence of anaerobic bacteria; this was found in 25% of women in the study. Ethnicities were evenly distributed across all CSTs.

Chlamydia acquisition was strongly associated with vaginal microbiota dominated by L. iners (CST III). Multivariate logistic regression analysis demonstrated that those women with L. iners-dominated CST had more than double the risk of chlamydia infection; odds ratio (OR) 2.6 (95% CI: 1.0-6.6;P = 0.04).

Age, education, ethnicity, mean age of first sexual contact, and number of sexual partners in the previous six months were not significantly associated with acquiring chlamydia infection.

 Lactobacillus species are commonly found in the vaginal environment, and they have previously been shown to have a protective role against other organisms that cause infections. It has also been shown that chlamydia infection in women is associated with depletion of Lactobacillus spp.

However, the findings of this study challenge our assumption that having predominantly Lactobacillus spp. in the vagina is protective.

The authors conclude that the specific species or possibly even the strain of Lactobacillus is important  in determining whether the vaginal microbiota can contribute to susceptibility to, or protection against, chlamydia infection.

Dr Richard Ma

van Houdt R, Ma B, Bruisten SM et al. Lactobacillus iners-dominated vaginal microbiota is associated with increased susceptibility to Chlamydia trachomatis infection in Dutch women. Sex Transm Inf 2018;94:117-23