In this illustration, new viruses emerge from an infected human throat cell. When you get the flu, viruses turn your cells into tiny virus factories that help spread the disease. Courtesy XVIVO/Zirus hide caption

itoggle caption Courtesy XVIVO/Zirus

Martha Martin of Durham, Maine, works three jobs and still can't keep up with her family's medical bills. She has medical insurance, but she and her husband can't make all of the payments. Emilie Sommer for NPR hide caption

itoggle caption Emilie Sommer for NPR