Despite Large Research Effort, H7N9 Continues to Baffle
 

Nearly a month after the first reported cases of people infected with the bird flu virus, many puzzles remain about how it made the jump to humans and adapted to us, how to prevent transmission, and how frequently an infection causes disease. As Science went to press, the number of laboratory-confirmed human infections had risen to 108, with 22 fatalities. One study suggests that H7N9 has spread widely in domestic birds in China, and a plan issued by China's Ministry of Agriculture calls for collecting samples from every poultry market and slaughterhouse in provinces with confirmed human cases, along with more limited testing in all other provinces. But there has been no direct contact with poultry in more than half the reported cases, and many challenges lay ahead.