The state famous for Mardi Gras is ground zero for the fight to educate teenagers about safe sex.

Louisiana's middle and high schoolers have some of the country's highest rates of pregnancy, HIV, syphilis, and other sexually transmitted infections (STIs). And thanks to a law that prohibits asking students about their sex lives, health care providers are hobbled in their search for answers.

"If we don't know what the behaviors are, we have no basis to develop policy or identify priorities," Freda Patterson, a public health researcher at Temple University, told BuzzFeed News.

Every two years since 1991, U.S. states have given public school kids between sixth and twelfth grades an anonymous questionnaire called the Youth Risk Behavior Survey (YRBS).

The questions cover all kinds of risky behaviors, from seatbelt wearing to drug use. The sexual behavior section includes questions about number of partners, contraceptive use, age of first sexual experience, and whether kids have been forced to have sex against their will.

To ensure that the survey responses can be compared to one another, each state must ask at least two-thirds of the original questions, and may also add their own. Four states have consistently refused to include questions about sex: Utah, Georgia, Virginia, and Louisiana.

"We wish that all four states would add sexual risk behaviors," Laura Kann, who manages the YRBS as part of her job at the Centers for Disease Control and Prevention, told BuzzFeed News. "It's important to have data on the sexual behaviors that kids practice."

Louisiana's reluctance stems from a 1993 law, which says that "students shall not be tested, quizzed, or surveyed about their personal or family beliefs or practices in sex, morality, or religion."

That law also says that sex education in Louisiana public schools must stress abstinence, and that teachers cannot distribute contraceptives.

"These are decisions that are best made by parents and local communities, not state government," Louisiana governor Bobby Jindal said in opposition to a 2014 state bill that would have introduced contraceptive use to sex ed curricula. That measure failed.

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