A Pakistani man wheels Jamshid, an 8-year-old girl with polio, around the outskirts of the capital Islamabad last July. Behrouz Mehri/AFP/Getty Images hide caption

itoggle caption Behrouz Mehri/AFP/Getty Images

Gilead Sciences' Truvada is a step closer to being approved as a way to prevent HIV infection. Paul Sakuma/AP hide caption

itoggle caption Paul Sakuma/AP

Nurse Susan Peel gives a whooping cough vaccination to a high school student in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness by the time people reach their teens and early adulthood. Rich Pedroncelli/AP hide caption

itoggle caption Rich Pedroncelli/AP

An electron micrograph of human norovirus. Charles D. Humphrey/CDC Public Health Image Library ID 10708 hide caption

itoggle caption Charles D. Humphrey/CDC Public Health Image Library ID 10708

Bartender Matt Carucci says he rarely feels safe biking in the city but often rides without a helmet anyway. "There are a lot of other ways to hurt yourself," he says. John Rose/NPR hide caption

itoggle caption John Rose/NPR

Noah Stewart shelters in the closet just 15 minutes before an April 2011 tornado demolished his house. Wearing the helmet may have saved his life, one doctor says. Courtesy of the Stewart family hide caption

itoggle caption Courtesy of the Stewart family

Kristen Miller talks over the risks and benefits of colonoscopy with Stephen Hanauer, chief of gastroenterology at the University of Chicago Medical Center. Brian Kersey/AP hide caption

itoggle caption Brian Kersey/AP

Doctors, don't order that CT scan when a less-expensive ultrasound would work just as well, the Choosing Wisely campaign advises. Catherine Yeulet/iStockphoto.com hide caption

itoggle caption Catherine Yeulet/iStockphoto.com

A package of K2, a concoction of dried herbs sprayed with chemicals sometimes called synthetic marijuana. New York moved to ban a wide range of products like these this week. Kelley McCall/AP hide caption

itoggle caption Kelley McCall/AP

Chhay Meth, 9, suffering through an attack of malaria at the family's home in O'treng village on the outskirts of Pailin, Cambodia, in 2009. A drug-resistant form of malaria in the region medical led officials to declare a health emergency. David Longstreath/AP hide caption

itoggle caption David Longstreath/AP

An artist on Rio de Janeiro's Copacabana beach puts the final touches on a sand sculpture of the assassin bug, which spreads Chagas disease. The sculpture was part of an event in 2009 commemorating the 100th anniversary of the discovery of the disease. Vanderlei Almeida/AFP/Getty Images hide caption

itoggle caption Vanderlei Almeida/AFP/Getty Images