Yeast infections are not sexually transmitted infections (STIs), and health experts don't know for sure if they are transmitted sexually. About 12 to 15 percent of men get an itchy rash on the penis if they have unprotected sex with an infected woman. If this happens to your partner, he should see a doctor. Men who haven't been circumcised are at higher risk.
Lesbians may be at risk for spreading yeast infections to their partner(s). Research is still being done to know for sure. If your female partner has any symptoms, she should also be tested and treated.
This answer is based on source information from the National Women's Health Information Center.