A young girl bathes in an irrigation canal. The canal and nearby river are the primary sources of water for most people who live in the country around Saint-Marc, Haiti. John W. Poole/NPR hide caption

itoggle caption John W. Poole/NPR

Health Department officials cull birds and put them in sacks after bird flu virus was detected in Bhubaneswar, India. Biswaranjan Rout/AP hide caption

itoggle caption Biswaranjan Rout/AP

The C. difficile bacteria causes infections that kill about 14,000 Americans each year, the CDC reports. CDC Public Health Image Library hide caption

itoggle caption CDC Public Health Image Library

An health official wearing protective gear culls a bird at a poultry farm after a naturally occurring bird flu virus was detected near Agartala, India, in January. Sushanta Das/AP hide caption

itoggle caption Sushanta Das/AP

Ramon Maldonado-Cardenas grimaces as he gets a flu shot from pharmacy student Khoa Truong during a health fair in Sacramento, Calif., last October. Rich Pedroncelli/AP hide caption

itoggle caption Rich Pedroncelli/AP

Nurse Susan Peel gives a whooping cough vaccination to a student at Inderkum High School in Sacramento, Calif., in 2011. Now it seems likely such shots will become routine for senior citizens, too. Rich Pedroncelli/AP hide caption

itoggle caption Rich Pedroncelli/AP

H5N1 avian flu viruses (seen in gold) grow inside canine kidney cells (seen in green). Cynthia Goldsmith/CDC hide caption

itoggle caption Cynthia Goldsmith/CDC

Virologists and other scientists are meeting at the World Health Organization's Geneva headquarters to talk about the bird flu. Pierre Virot/WHO hide caption

itoggle caption Pierre Virot/WHO

Students at a University of London class in Mexico City wear masks to protect them against swine flu in May 2009. High schools and universities closed by the pandemic had just reopened across Mexico. Brennan Linsley/AP hide caption

itoggle caption Brennan Linsley/AP

Inattention to catheters used often in ICUs can lead to serious infections. iStockphoto.com hide caption

itoggle caption iStockphoto.com