elizabeth hurd just filed this from dallas. >> reporter: it was the news america had been dreading. >> an individual traveling from liberia has been diagnosed with ebola in the united states. >> reporter: the centers for disease control confirming the first case of ebola in the u.s. a patient who recently travelled from liberia to dallas is sick with the disease. the unfiidentified man is critically ill and has been in the hospital since sunday. he began feeling sick four or five days after arriving in the u.s. >> the likelihood for this individual to have spread it on an airplane is zero. he had no symptoms while traveling. >> reporter: the head of the cdc is optimistic they will control ebola from spreading. >> the bottom line here is that i have no doubt that we will control this importation, or this case of ebola so that it does not spread widely in this country. >> reporter: health authorities have begun tracking down family and friends who may have had close contact with the patient and could be at risk of contracting the virus. >> follow them for 21 days, if they develop a feve