CHICAGO, Illinois (AP) -- At least one in four teenage girls nationwide has a sexually transmitted disease, or more than 3 million teens, according to the first study of its kind in this age group. 

For many, the numbers most likely seem "overwhelming because you're talking about nearly half of the sexually experienced teens at any one time having evidence of an STD," said Dr. Margaret Blythe, an adolescent medicine specialist at Indiana University School of Medicine and head of the American Academy of Pediatrics' committee on adolescence.