The University of Nebraska Medical Center said on Monday all 18 U.S.-resident passengers from the hantavirus-hit MV Hondius cruise ship have returned to their home states after completing monitoring at its National Quarantine Unit.

Sixteen of those passengers arrived on May 11 following their trip on the cruise ship associated with a hantavirus outbreak, it said. Two more former passengers arrived at the National Quarantine Unit on May 15.

“No cases of hantavirus disease occurred in the United States as a result of this outbreak,” the U.S. Centers for Disease Control and Prevention said.

Earlier this month, eight U.S. residents returned to their home states following three weeks of monitoring at the National Quarantine Unit. Ten others were under observation.

The World Health Organization recommends monitoring and quarantining high-risk contacts for 42 days after exposure, while advising low-risk contacts to self-monitor and seek medical care if symptoms develop.