Brent K. Newell, a Washington, D.C.-based epidemiologist working in Cairo and the deputy chief medical officer of the CDC, said the Hainan cruise passengers were returning home, many of them with more than 300 confirmed cases of the deadly coronavirus.

“People should not worry that the virus is circulating again and we expect to see more cases of coronavirus. Our teams are watching this, but we’re not anticipating an epidemic,” Dr. Newell said at a news conference. He added that the cases of the sickness being brought back to the United States appear to be under control. New evidence suggests the virus is not transmittable among healthy people, he said.

“The result of the pneumonia from this very, very severe infection is extensive diarrhea. We did not, however, get any infections of the lung. We did not, however, see people die, and what we’re doing is we’re monitoring closely. What we’re finding is that antibiotics and antivirals do generally relieve the symptoms, but sometimes we get cases where people need to go back to the hospital to treat their pneumonia,” he said.

World Health Organization experts have said that it is not clear if there has been transmission from a contaminated poultry farm, but its experts are still investigating.

“We think that these cases were from the poultry farm,” Dr. Newell said.