Seventeen percent of people in the U.S. had the genital herpes virus from 1999 to 2004. This is down from the 21 percent who had it from 1988 to 1994.
The Centers for Disease Control and Prevention based its study on blood samples rather than self-reporting.
The CDC findings support other studies which found reductions in risky sex among teenagers.
Genital herpes is normally contracted through intercourse with a person who has infected sores, but it can also spread through oral or anal sex.
Herpes cannot be cured. Therefore a decrease in the nationwide infection rate means fewer people are getting HSV-2 infections, according to the study.
The researchers suggest the decrease may be a result of more careful partner selection, an increase in the use of condoms and choosing oral sex over vaginal sex.
