Health officials are closely monitoring the passengers from the cruise ship that was hit by a deadly hantavirus outbreak, as they have returned to their home countries. Some passengers were moved into isolation after positive tests.

About 150 people were on the ship, the MV Hondius, when it anchored off Spain’s Canary Islands on May 10. Passengers and most crew members were evacuated that day.

The World Health Organization has said that the risk to the general population is low, but health officials around the world are trying to calm fears and control potential spread by keeping track of people who were aboard or in close contact with those who were.

On May 10, the U.S. Department of Health and Human Services said that one of 18 Americans who had been returned to the United States from the ship “tested mildly” positive for the Andes form of the hantavirus, while another had “mild symptoms.”

On May 14, U.S. health officials said they were monitoring an 16 additional people across the country for symptoms of hantavirus whom the Centers for Disease Control and Prevention had not previously mentioned.

The new total of those being monitored in the United States was 41 as of May 14. They were quarantining at special facilities in Omaha and Atlanta.