virus. what we don't know is how sustained the transmission is. >> reporter: signs of the virus include fever, cough, and trouble breathing. in severe cases, patients suffer pneumonia, kidney failure, and death. there are no vaccinations. china was criticized for underovirus pandemic that killed nearly 800 people in 2002/2003, but the c.d.c. says china's prompt reporting of this new virus helped them detect the first case here in the u.s. >> the global community and the united states have been preparing for exactly this situation. >> reporter: this is the international terminal at atlanta's airport, which today became one of six in the u.s. to start screening arrivals from asia for the virus. the challenge: this virus incubates slowly. someone could have it and not know it for days after getting home. norah? >> o'donnell: and that is what is so scary for many people. mark, thank you. tonight freeze warnings are