Background The pathogenesis of BV is poorly characterised although there is considerable evidence that it is sexually transmitted. Some have suggested that the alkalinity of semen may be a factor. We report a case of suspected sexual transmission of BV from a prostatectomized male to a female.

Methods Case report from a prospective study of behavioural factors influencing the vaginal flora wherein women collect daily self-obtained vaginal slides and behavioural data. Slides are Gram stained and interpreted according to Nugent criteria. Women are encouraged to present for evaluation if symptoms occur.

Results A 51 year old female complained of new onset vaginal irritation for one day. She denied discharge, pruritus, or odour and had not recently douched. She was sexually active with one partner, a male who had undergone a radical prostatectomy. Her last unprotected intercourse occurred 3 days prior to onset of symptoms and prior to that she had been abstinent for 6 weeks. A slide obtained the day before her sexual exposure had a Nugent score of 0. Repeat gramme stain revealed BV with a Nugent score of 8. Her male partner admitted to unprotected sex 6 days prior to their encounter with another female. A vaginal slide obtained from that partner revealed BV with a Nugent score of 8.

Conclusion To our knowledge, this is the first report documenting sexual transmission of BV from a male to a female in the absence of semen. The onset of symptoms and her sexual history indicates that the incubation period for BV was 72 hours. It is likely that the patient’s male partner became colonised in his distal urethral or coronal sulcus with BV organism(s) after he had unprotected sexual intercourse with his other female partner and transferred those organism(s) on desquamated epithelial cells to our patient during unprotected sex.