The number of hantavirus cases linked to the MV Hondius cruise ship has risen to 11, as American passengers remain under quarantine at the University of Nebraska Medical Center (UNMC) in Omaha, Nebraska. Global health officials warn that case numbers may continue to grow due to the virus’s long incubation period, which can last up to 42 days.

Among those quarantined is Jake Rosmarin, who spoke to NBC News from his room at UNMC, saying he feels reassured by the care provided and has not shown symptoms or tested positive for hantavirus. He and 15 other Americans arrived in Nebraska on Monday after being evacuated from the cruise ship, which had departed Argentina on April 1 with nearly 150 people on board. Two other Americans are being monitored at Emory University Hospital in Atlanta.

The outbreak resulted in three deaths—a Dutch couple and a German national. The World Health Organization (WHO) is investigating the source, focusing on a bird-watching trip in southern Argentina taken by the first passenger who died. Lab results have confirmed nine cases of the deadly Andes hantavirus strain, with two additional suspected cases. While the Andes strain can spread between people, transmission usually requires close and prolonged contact, and experts stress the risk to the general public remains low.

Passengers from the MV Hondius were evacuated to several countries, including the United States, Spain, France, and the United Kingdom. In the U.S., the Department of Health and Human Services stated that anyone not showing symptoms would remain under observation for several days before being allowed to self-isolate at home. Those who are symptomatic or test positive are being cared for in specialized biocontainment units, including at UNMC—the only federally funded quarantine unit of its kind in the country, designed for high-consequence infectious diseases. According to a UNMC statement, the facility is fully equipped to monitor and treat potentially exposed individuals while ensuring community safety.

UNMC and Nebraska Medicine leaders emphasized their preparedness, having previously managed patients during the 2014 Ebola outbreak and the early stages of the COVID-19 pandemic. Governor Jim Pillen praised the coordination between state and federal agencies, stating Nebraska is committed to supporting national efforts and remains in communication with President Trump and federal health authorities.

Passengers will continue to be monitored for symptoms over the full incubation period. The CDC expects most will be able to return home for self-isolation and daily monitoring.