People ages 15-24 acquire nearly one-half of all new sexually transmitted diseases, U.S. health officials say. A report by the Centers for Disease Control and Prevention's National Center for Health Statistics -- "Teenagers in the United States: Sexual Activity, Contraceptive Use, and Childbearing, 2006-2010 National Survey of Family Growth" -- found the rates of syphilis among female and male teens are lower than those of other age groups but the rates have increased every year since the early 2000s. The report estimated the direct medical cost of the STD among those ages 15-24 was at least $6.5 billion in 2000. The researchers suggest that while representing 25 percent of the sexually experienced population, those age 15-24 acquire nearly one-half of all new STD, the report said. From 2006 to 2010, 41 percent of female teens and 31 percent of male teens said they didn't have sex because it was against religion or morals. For females in 2006-2010, 18 percent said they didn't have sex because they didn't want to become pregnant and 19 percent said they hadn't found the right person. Thirteen percent of male teens said they didn't have sex because they didn't want to make anyone pregnant, but less than 7 percent of males and females said they didn't have sex because they didn't want to get a sexually transmitted disease.