Complex sentence: The study of 838 girls who participated in a 2003--04 government health survey found the highest overall prevalence among black girls, nearly half in the study were infected, compared with 20 percent among both whites and Mexican-American teens.
Split into simpler sentences: The study of 838 girls who participated in a 2003--04 government health survey found the highest overall prevalence among black girls; nearly half in the study were infected. This is compared with 20% among both whites and Mexican-American teens.