Anal condyloma causes and treatment

Patient: My partner of 8 years has contracted anal (only) warts in the last year. He assures me he is strickly heterosexual. I was tested for HPV and am negative. Can I beleive him? How else can this be contracted? Thank you for your time.

Doctor: He does not have to have anal intercourse to get anal warts. He should get tested for HPV as well.