Ricardo "Cobe" Williams, wearing the cap, served time for attempted murder before joining CeaseFire as a "violence interrupter." Above, he talks with Lil Mikey in a scene from the documentary The Interrupters. Lil Mikey, who'd also been in prison, went on to become an outreach worker with the organization. Aaron Wickenden/Courtesy of Kartemquin Films hide caption

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Louis Arevalo holds his Truvada pills at his home in Los Angeles. The drug can be over 90 percent effective at preventing spread of HIV. Heidi de Marco/Kaiser Health News hide caption

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The bar chart tells all: That's how eighth-graders at Bakgatle Community Junior Secondary School in Botswana can compare the HIV infection rate of older men and of teenage boys. Don Boroughs for NPR hide caption

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In a study in Lesotho, the prospect of earning a cash prize in a lottery motivated young people to practice safe sex. iStockphoto hide caption

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Austin, Indiana's needle exchange program is open for business this week, but health workers worry the program will be tough to quickly replicate in other counties. Darron Cummings/AP hide caption

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Volunteer Patrick Pezzati searches yards in Turners Falls, Mass., for discarded heroin needles. Karen Brown/WFCR hide caption

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In Philadelphia, some drug users are selling clean needles from needle exchange programs on the street. Researchers say the black market isn't necessarily a bad thing. ImageZoo/Corbis hide caption

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