Background NGU is common with no known etiology in ∼50% of cases. We evaluated the association of urethral bacteria with NGU among men who have sex with men (MSM) and men who have sex with women (MSW).

Methods Urine samples were collected from MSM and MSW attending a Seattle STD Clinic and enrolled in a cross-sectional study. Chlamydia trachomatis (CT) and Mycoplasma genitalium (MG) were detected by TMA (Aptima), and adenovirus, HSV-1 and HSV-2 by PCR. NGU was defined as having urethral symptoms or visible discharge and ≥5 PMNs/high powered field (HPF). Absence of CT, MG, adenovirus, and HSV was considered as idiopathic NGU. Men without NGU had no urethral symptoms, no discharge, and <5 PMNs/HPF. Broad-range 16S rRNA gene PCR with deep sequencing was used to characterize the urethral microbiota. Compositional lasso analysis of bacterial taxa was conducted to identify associations between bacteria and NGU; beta coefficients (β) giving change in probability of NGU per log2 change in relative abundance are reported.

Results Of 434 (199 MSM, 235 MSW) urine samples, 330 yielded sequence data. NGU+ men were less likely to yield sequence data (70% vs 84%, Fisher’s p=0.001). Of 328 men with ≥1000 sequence reads/sample, 95 MSM (44 NGU+) and 143 MSW (46 NGU+) were negative for CT, MG, adenovirus, and HSV. Higher relative abundances of Haemophilus influenzae (β=0.0139) and Mycoplasma penetrans (β=0.0095) were positively associated with idiopathic NGU in MSM, while H. influenzae was positively associated with idiopathic NGU in MSW (β=0.0184). The model also identified bacterial species that were negatively associated with NGU in MSM and MSW. Notably, Lactobacillus iners was negatively associated with idiopathic NGU in MSW (β=−0.0006) but not MSM.

Conclusion Different bacterial species are associated with NGU in MSM and MSW. We identified two bacterial species infrequently detected in the male urethra as positively associated with NGU.

Disclosure No significant relationships.