In the most cases Gardnerella Vaginalis is caused by unprotected sexual intercourse. Man cannot pass infection to women but in some cases women can pass infection to a partner. If you are in stable relationship you need to be faithful and do not have sex with others. Gardnerella could be caused by vaginal douching and using IUD as a form of contraception. If you are doing douching you can damage your good bacteria and infection will back more often.