It’s what I recall from medical school. I graduated in ‘10 so numbers may have changed. You’ll find different quotes from different studies (like the planned parenthood I linked said something different). For more info I would search pubmed or ogle scholar if you want details re: how a particular study was conducted.

An important thing to keep in mind is that a lot of people with genital herpes have never had an outbreak and are unaware they have it. This is why we screen all pregnant women at their prenatal visits, because there is potential for pretty devastating complications for an infant born to an HSV mother vaginally should she happen to have said first outbreak around the time of delivery. Stress provokes outbreaks, so there ya go.