Behavior: A Snapshot of Teen Sex

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The study shows how easily STDs could spread in a high school, but paradoxically, it also indicates how easily the chains of contagion could be snapped. "If you could get person A or B to change his or her behavior--through abstinence, using a condom, or getting treated for an STD--then you could prevent transmission from B to C and down the network," says Kathleen Ethier, of the CDC's Division of STD Prevention. It's much harder to intervene in the adult core-transmitter model. So, scary as that map may look to parents, Ethier says, understanding how it works "is very encouraging for us." •