An Unusual Case of Unexplained Infertility: Co-colonization of the Uterus and Seminal Fluid

Chronic endometritis (CE) is defined as a persistent, mild inflammation of the endometrium induced by intrauterine bacterial infection. CE has been associated with infertility in patients with recurrent in vitro fertilization (IVF) failure. We report an unusual case of bacterial co-colonization of the endometrium and seminal fluid in a couple with unexplained infertility.  A 35-year-old woman presented to the office for infertility evaluation after 16 months of inability to conceive naturally using ovulation kits. Initial workup revealed adequate ovarian reserve with an anti-Müllerian hormone (AMH) level of 4.8 ng/mL, tubal patency on hysterosalpingogram, and normal semen analysis. The patient and her partner failed to conceive following three cycles of ovulation induction with intrauterine insemination (IUI). In preparation for IVF, an endometrial biopsy (EMB) was performed, and five CD138+ plasma cells per 10 high-power fields suggested CE. The patient underwent antibiotic therapy, yet EMB remained positive. At this time, the partner's semen culture was positive for Enterococcus faecalis and Escherichia coli. Endometrial microbiome metagenomic analysis (EMMA) and analysis of infectious chronic endometritis (ALICE) demonstrated co-colonization with the same bacteria seen on her partner's semen culture. Both the patient and her partner required multiple rounds of antibiotic therapy before successful conception via IVF. This case demonstrates an unusual occurrence of bacterial co-colonization of the endometrium and seminal fluid in a couple with unexplained infertility, suggesting a potential pathway for CE development from bacteriospermia. The patient's EMMA/ALICE tests and the partner's semen cultures revealed the presence of the same bacteria. While current literature does not identify the development of CE from the bacteria in a partner's semen, there is an association between bacteria in semen and infertility.  In couples with unexplained infertility, thorough evaluation for CE with EMB and EMMA/ALICE can be performed in conjunction with a semen culture on the partner to explore potential co-colonization and guide dual-partner treatment.