Hantavirus live updates: 16 at facility in Nebraska, 2 at hospital in Atlanta

Twelve U.S. residents are under monitoring by state health departments for hantavirus, according to officials. None of these 12 people have symptoms, officials said.

Seven of the 12 were cruise ship passengers who disembarked before the outbreak was declared: two are in Texas, two are in Georgia, one is in Virginia, one is in Arizona and one is in California.

The other five people were exposed to an infected individual during air travel, officials said. Two are in New Jersey, two are in Maryland and one is in California, officials said.

The Maryland Department of Health said it is monitoring two residents who were on an overseas flight with a MV Hondius cruise ship passenger who later tested positive for the hantavirus.

Health officials said the monitoring is out of an abundance of caution and that the risk to the public is very low.

"No hantavirus cases have been identified in Maryland since 2019. Andes virus infections have never been reported in Maryland," the Maryland Health Department said.

California health officials on Monday released new information about four residents who were exposed to the hantavirus and are now being monitored, all of whom are currently healthy and not showing symptoms.

A South Bay resident from Santa Clara County was on the MV Hondius cruise ship but disembarked before the outbreak. Two other Californians were also on the ship and disembarked over the weekend in the Canary Islands. They are now in quarantine at a federal facility in Nebraska.

The fourth Californian, a Sacramento County resident, has returned home. That person was not on the ship but was exposed to someone who was ill on a plane in South Africa, according to health officials.

All four individuals are being closely monitored.

In the coming days, as the cruise ship passengers decide whether to stay at the University of Nebraska quarantine facility or self-monitor at home, those who opt to go home will not fly on a commercial flight, an official from the Centers for Disease Control and Prevention told ABC News. Passengers who opt to go home will have been assessed by health officials for any signs of illness.

-ABC News' Youri Benadjaoud