A woman wearing a mask rides past a KFC restaurant in Shanghai last month. Food scares and the bird flu haven't stopped many chicken lovers in the city from visiting KFC and other restaurants. Aly Song/Reuters /Landov hide caption

itoggle caption Aly Song/Reuters /Landov

Scientists in the U.S. are growing the H7N9 virus in the laboratory to help with vaccine development. James Gathany/CDC/Douglas E. Jordan hide caption

itoggle caption James Gathany/CDC/Douglas E. Jordan

A health worker collects pigeons from a trap at People's Square in Shanghai, China, earlier this month. So far, workers have tested more than 48,000 animals for the H7N9 flu virus. ChinaFotoPress/Getty Images hide caption

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A vendor weighs a live chicken at the Kowloon City Market in Hong Kong Friday. Health authorities there have stepped up the testing of live poultry from China to include a rapid test for the H7N9 bird virus. Lam Yik Fei/Getty Images hide caption

itoggle caption Lam Yik Fei/Getty Images

People sit near pigeons at a park in Shanghai Sunday. A new strain of bird flu has spread from eastern China to other provinces, with 13 deaths reported. AP hide caption

itoggle caption AP

A child wears a mask near a closed section of a poultry market in Shanghai, where health workers detected the new bird flu, H7N9. Eugene Hoshiko/AP hide caption

itoggle caption Eugene Hoshiko/AP