Everything I’ve seen says sexually transmitted:
http://www.cdc.gov/std/HPV/STDFact-HPV.htm
http://www.ashastd.org/hpv/hpv_learn_fastfacts.cfm
http://www3.niaid.nih.gov/healthscience/healthtopics/human_papillomavirus/transmission.htm
http://www.nlm.nih.gov/medlineplus/hpv.html
http://www.webmd.com/sexual-conditions/hpv-genital-warts/default.htm
It’s definitely sexually transmitted. However, this TV show discussed the disease in detail, and the expert who was interviewed made a statement to the effect that, “In fact, you don’t even have to have sex to get it.”
She stated that physical contact short of sex could do it.