How would we definitively know?
There is a long list of activities which could have infected us; getting nails done, dentistry, participation in contact sports, hair cuts, tattoos, military service, innoculations, various types of drug use, miscellaneous types of domestic contact (toothbrush, razor, fighting. tending or being tended to of injuries), and oh yes..... has anyone ever had medical care? People have been known to have been infected in all varieties of medical settings; receiving blood products, anything IV, through surgeries, and through seemingly benign medical exams such as colonoscopies.
Now..... even assume that you had none of the above but still had had sex with another HCV infected partner.....it still wouldn't prove that you had caught it through sexual relations. In the past that was thought to have possibly been the case but in some sexual transmission studies they found that some partners *assumed* to have transmitted has discordant genotypes or quasispecies. (ie; the partner with a geno 1 did not transmit a genotype 3 infection, no matter how HOT and heavy the sex action was)
The only way of knowing would be to follow people around and test them for antibodies and PCR's after every risk event. To some extent the statistics can point towards probable methods of transmission, though.
best,
Willy
I have heard it's rare, would need to be very rough sex with tearing and bleeding going on.