It is being called a medical mystery. It is a virus that starts like a cold but can become deadly.
The adenovirus is known mostly for causing colds and pink eye.
It spreads through contact and the air we breathe.
This year it's infected more than a thousand Americans in a handful of states including Texas, and at least 10 patients have died from it.
Sophisticated diagnostic tests can identify adenovirus within hours but doctors stress the key is recognizing its symptoms before they become life threatening.