Dr. Lisa Sterman held a Truvada pill at her office in San Francisco in 2012. She prescribed Truvada to patients at high risk for HIV infection even before the Food and Drug Administration approved the medicine explicitly for that purpose. Jeff Chiu/AP hide caption

itoggle caption Jeff Chiu/AP

John Hartigan, proprietor of Vapeology LA, a store selling electronic cigarettes and related items, takes a puff from an electronic cigarette in Los Angeles. Reed Saxon/AP hide caption

itoggle caption Reed Saxon/AP

The Centers for Disease Control and Prevention's PulseNet service monitors clusters of sickness linked to potentially dangerous strains of foodborne pathogens such as E.coli or salmonella. Reed Saxon/AP hide caption

itoggle caption Reed Saxon/AP

The Eagle Mountain Church in Newark, Texas, was linked to at least 21 cases of measles this year, mostly in children. LM Otero/AP hide caption

itoggle caption LM Otero/AP

Small declines in obesity among young kids could help stem bigger problems in the future. Ocean/Corbis hide caption

itoggle caption Ocean/Corbis

A new study from the Centers for Disease Control and Prevention finds no link between the number of vaccinations a young child receives and the risk of developing autism spectrum disorders. Jeff J. Mitchell/Getty Images hide caption

itoggle caption Jeff J. Mitchell/Getty Images