The case of a Pennsylvania girl who is dying from cystic fibrosis has sparked an emotional debate over how the nation allocates lungs for transplantation.
Ten-year-old Sarah Murnaghan is in intensive care at Children's Hospital of Philadelphia awaiting a lung transplant. Under the current rules, lungs from adults are offered to other adults and adolescents before being offered to children younger than 12.
Here's a sobering thought: Wild birds — including city pigeons and ubiquitous Canada geese — carry 170 different types of bird flu. You know, all those viruses with the Hs and Ns in their names, like H1N1 and H5N1.
Only a dozen of these viruses have infected humans so far, but many of those have been deadly, and three of them have caused global flu pandemics.
Does every bird flu that leaps into people have the potential to turn into the next "big one" that spreads rapidly around the world?