The 18 American passengers exposed to hantavirus aboard the MV Hondius cruise ship are under quarantine at a hospital in Omaha, receiving care as they await a decision on how long they will need to remain there.

Elsewhere, a 12th illness linked to the vessel was confirmed Friday in the Netherlands as health officials continue tracking hundreds of people who may have been exposed.

The physician overseeing the National Quarantine Unit at the University of Nebraska Medical Center said Friday that none of the American patients are showing symptoms. Dr. Michael Wadman referred questions to the Centers for Disease Control and Prevention on whether the group will need to complete the full 42-day quarantine period.

The CDC did not respond Friday to inquiries about the plan for the passengers, who are being housed in specialized rooms designed to resemble hotel accommodations, complete with exercise equipment and small refrigerators. The units use negative-pressure ventilation and waste sterilization systems to prevent any potential spread of infection.

Hantavirus typically spreads through contact with rodent droppings and is not easily transmitted between people. However, the Andes virus identified in the cruise ship outbreak may spread between humans in rare cases. Symptoms usually appear one to eight weeks after exposure. Health officials recommended the extended quarantine due to the virus’ incubation period.

Wadman said that once the passengers realized how long they would be staying in quarantine, they began ordering items they needed after health officials allowed them to bring only a small plastic bag of belongings when they left the MV Hondius. They were required to leave their luggage behind, leading to a steady stream of packages arriving at the quarantine unit after the group began reaching Omaha on May 11.

Between twice-daily symptom checks, staff at the nation’s only dedicated quarantine unit are working to help passengers pass the time with special meals featuring local food trucks and Nebraska specialties such as Runzas, along with educational sessions on the sandhill crane migration that brings millions of birds to the state each spring.

The rooms also have high-speed internet access, allowing passengers to connect virtually with family and friends. Jake Rosmarin said it can be lonely at times being far from his fiancée in Boston, but the days have largely passed quickly as he calls relatives and posts travel videos to his Facebook and Instagram accounts. He said he is trying to stay positive rather than focus on nearly another month in quarantine.

"Why am I going to harp on those negative aspects? The time’s just going to go by slow if I harp on the negatives,” he said.

Rosmarin said he is grateful for the care provided by nurses and doctors from the medical center and Nebraska Medicine hospital, who volunteer at the quarantine unit, noting simple comforts such as his preferred Starbucks iced horchata with oat milk and vanilla cold foam.

"They’ve just been amazing. Truly, truly, truly. I think they’ve gone above and beyond in making sure that we’re comfortable here,” Rosmarin said. He also ordered a new mattress pad and pillows, along with Mixtiles photos of himself and his fiancée, to make the room feel more like home.

Rosmarin and several other passengers briefly left their rooms Sunday evening during a tornado warning in Omaha, though they wore masks and maintained distance while medical staff wore full protective gear.

The hospital plans to offer passengers a Runza meal Tuesday and Omaha Steaks on Thursday. Rosmarin said he ordered a barbecue bacon Runza, a sandwich made with meat, seasonings and sauce baked inside bread. The regional chain is largely limited to Nebraska, though similar dishes are known elsewhere as bierocks.

Nebraska Gov. Jim Pillen, who owns a large hog farm, said at a Friday news conference that he hopes to arrange a pork tenderloin dinner if hospital chefs can prepare it properly.

Wadman said the passengers remaining in Omaha have been cooperative, despite a formal order earlier this week from the CDC preventing two of them from leaving the quarantine unit.

"I think there’s many that would really like to be home,” Wadman said, though it remains unclear whether the CDC will allow release before the 42 days are complete. Each case will be evaluated individually.

Twelve people worldwide who were aboard the MV Hondius have fallen ill, including a crew member confirmed Friday in the Netherlands. Three people have died, including a Dutch couple whom health officials believe were among the first exposed while traveling in South America. No additional deaths have been reported since May 2, according to World Health Organization (WHO) Director-General Tedros Adhanom Ghebreyesus.

"We continue to urge affected countries to monitor all passengers and crew carefully for the remainder of the quarantine period. More than 600 contacts continue to be followed in 30 countries, and a small number of high-risk contacts are still being located,” he said.

University of Nebraska President Jeffrey Gold said the new cases will be considered as public health officials determine quarantine length, though the CDC is making the final decision.

"Any case, any symptoms, any positive test anywhere gives us more information about the biology of this viral illness. And as any good scientific approach would, it influences our decision-making,” Gold said.