Quarantine was lifted on Sunday for American passengers of a cruise ship that was hit by a deadly hantavirus outbreak. The passengers had been held for weeks at a federal facility in Nebraska.

The day marks a return to day-to-day life for all 18 passengers, including the six who had stayed at the National Quarantine Unit at the University of Nebraska Medical Center until the end of the 42-day period. They were released without fanfare. Since the end of May, 12 had been released from the unit to home confinement.

No cases associated with the cruise outbreak had been confirmed in the U.S. as of Thursday, the U.S. Centers for Disease Control and Prevention said in an update.

The outbreak occurred on the MV Hondius, a cruise ship that began its route in Argentina in April. The European Center for Disease Prevention and Control said that as of June 17, 13 cases of hantavirus had been reported from the ship. Three passengers died. The World Health Organization identified the strain as the Andes subtype, which can be transmitted between people who have close contact with each other.

There were 16 American passengers from the ship who started quarantining in Omaha in May. Two others joined them after beginning their quarantines in Atlanta.

Two-thirds of the group trickled out of the quarantine unit in Nebraska after May 31 to finish their isolation at home, under government surveillance. Others chose to stay through the duration of the 42-day quarantine period.

One woman, who remained in the unit, said she was forced to stay in the quarantine unit against her wishes.

Robert F. Kennedy Jr., the secretary of health and human services, signed an order to keep the woman, Angela Perryman, at the facility, despite the recommendation of a C.D.C. medical review that she be allowed to return to her home in Florida.

Ms. Perryman, 47, had tested negative for the virus and said she had no symptoms. She’d previously challenged an order that blocked her from leaving before the end of May.

She said on Sunday morning that she was prepared to fly home on a commercial flight with no restrictions. But Ms. Perryman said she planned to continue speaking out against Mr. Kennedy’s decision, which she said was an act of political retaliation.

“My duty as an American citizen is to fight this,” she said.

Her lawyers, Steve Hyman and Norman Siegel, said they were considering litigation.

“I think that Angela is a symbol of injustice,” Mr. Siegel said. “She resisted, she stood up and challenged injustice, specifically the conditions of a government-imposed quarantine that was and continues to be legally indefensible and medically unsupported.

“Perhaps Angela’s story will change how our federal government handles quarantines differently in the future,” Mr. Siegel said. “The good news today is Angela is going home.”

Multiple emails to a spokeswoman for the Department of Health and Human Services over the past week requesting comment about the end of quarantine have received no response.

At least seven other Americans left the cruise ship earlier in its passage than the group that was quarantined in Nebraska. They were monitored by state and local health departments for 42 days until June 6, and no cases of hantavirus were detected, the C.D.C. said.

Hantavirus, a family of viruses carried by rodents, is rare but deadly. The disease normally causes flulike symptoms that develop up to six weeks after exposure, and can become more severe when the virus infects blood vessels and they leak fluid into the lungs.

Fewer than 900 cases of hantavirus disease had been confirmed in the country by the end of 2023 since surveillance began in 1993, according to the C.D.C.