For the first time, the Middle East Respiratory syndrome or MERS has spread person-to-person in the United States.
Health officials say an Illinois man contracted the virus after two short business meetings with an infected man from Indiana.
Their only physical contact was a handshake. Now, the Centers for Disease Control and Prevention (CDC) wants to test everyone this man came into contact with.
MERS, which originated in Saudi Arabia, kills about 30 percent of its known patients.
Dr. Sanjay Gupta is OutFront with the latest.