The CDC is investigating a mysterious bacterial disease, known as melioidosis that’s killed two Americans and sickened two others.  The cases, which were diagnosed between March and July, occurred in Kansas, Texas, Georgia and Minnesota. The bacteria that causes the disease grows in the tropic, but the four people affected hadn’t traveled outside the U.S.  The CDC believes there’s a common source for all four cases and is working on figuring out what it is.