in case you are wondering, is awfully steep.
"scientists reconstructing the genetic evolution of the deadly virus say they have traced its true path -- concluding that the insidious pathogen used Haiti as a steppingstone from Africa to the United States and arrived much earlier than had been thought. It then simmered silently here for more than a decade before it was detected, beginning its global spread along the way.
from Africa, to Haiti, to the world. "The United States probably served as a worldwide hub for this spread."