Fifteen passengers were welcomed to the University of Nebraska Medical Center’s quarantine unit Monday morning and one person is in the biocontainment unit, according to the unit’s medical director, Dr. Mike Waldman.

The quarantine unit is more like a hotel, while the biocontainment unit is patient-based care, more like a hospital, officials said.

The 15 passengers at the quarantine unit are in “good spirits,” Waldman said.

“We’ve been doing symptom monitoring, as well as temperature checks," he said. "Everyone here is asymptomatic and ... do not have a temperature at this time. They're all resting now and we'll do further assessments later in the day, once they've had a chance to sleep."

The one person in the biocontainment unit is doing well and does not have symptoms, but is “very tired” after a “really long journey,” officials said.

Besides the 16 cruise ship passengers in Nebraska, two cruise ship passengers were flown to Atlanta “for further assessment and care," officials said.

The two patients in Atlanta "are under medical evaluation," officials said, though it is not clear why those two patients traveled to Atlanta.

The “risk of hantavirus to the general public remains very, very low,” Dr. Brian Christine, Assistant Secretary for Health at the Department of Health and Human Services, said at a news conference on Monday.

The Andes variant "does not spread easily, and it requires prolonged, close contact with someone who is already symptomatic," he assured.

Even though, he said, the department has taken the situation "very seriously from the very start."

Initial genetic analyses confirmed that the hantavirus on the Hondius cruise ship is of the "known Andes variant and rule out any relevant mutations," Spanish Health Minister Monica Garcia said in a post on social media.

-ABC News’ Victoria Beaulé

Jan Dobrogowski, the captain of the Hondius, recorded a message thanking passengers and crew for their patience during the “extremely challenging” last few weeks.

“What touched me the most, what moved me the most, was your patience, your discipline, and also kindness -- kindness that you show to each other. ... I've witnessed your caring, your unity and quiet strength," Dobrogowski said, according to the Associated Press.

He added, “Our thoughts are with the ones that are no longer with us. ... This can be very painful to the people on board, especially already dealing with grief, worry and perhaps uncertainty.”

The CDC is alerting doctors and health departments around the country to be aware of the potential for imported hantavirus cases from the cruise ship outbreak.

The agency notes that the risk of broad spread to the United States is considered extremely unlikely at this time.

There have been no confirmed hantavirus cases associated with the cruise ship in the U.S. and at least nine residents are being monitored across six states, but none have shown any signs of illness at this time.

The CDC’s advisory to doctors, via the Health Alert Network (HAN) system, reminds them that in the event of a potential hantavirus case, patients should be placed in an isolated room and health care providers should use a gown, gloves, eye protection and an N95 mask or higher level respirator.

Doctors should also consider hantavirus infections as a potential diagnosis if a patient presents with hantavirus symptoms as well as known contact with an infected individual, officials said.

-ABC News' Youri Benadjaoud