Sixteen passengers evacuated from the cruise ship linked to the growing Andes hantavirus outbreak are now being monitored inside Nebraska Medicine’s highly specialized federal quarantine unit—the only facility of its kind in the United States. The unit, designed to contain some of the world’s deadliest infectious diseases, previously treated Ebola patients and some of the first Americans infected with COVID-19 aboard the Diamond Princess cruise ship.

As health officials race to contain the outbreak, one repatriated passenger has tested “mildly PCR positive” for the Andes strain of hantavirus, according to the Department of Health and Human Services, while another has developed mild symptoms. The Andes strain is the only known hantavirus capable of spreading from person to person.

TIME spoke with Dr. Michael Ash, CEO of Nebraska Medicine, about how the quarantine unit operates, how staff prevent the virus from escaping containment, and what experts currently understand about the risks posed by the Andes strain.

The conversation below has been edited for clarity.

What happens to these passengers in the first 24 hours at the biocontainment unit? 

MA: Currently, anyone who developed symptoms would be transported to one of the other biocontainment units to maintain our capacity. Our quarantine unit can host 20 asymptomatic individuals with individual oxygen air exchange systems, so each person is very safely monitored in that room. If they become ill, they are transferred to the health system and to our biocontainment unit that is able to provide care all the way up to intensive care. That is a smaller unit, and it's a much more intensive unit. So we wanted to protect as much capacity as we could. 

Of the sixteen Americans that came to University of Nebraska Medical Center, one had tested positive in another country. That individual is displaying no symptoms. Out of an abundance of caution, they were transferred to our biocontainment unit. The 15 asymptomatic patients who tested negative were put into quarantine. Each individual has their own room with a dedicated air supply, and all air exiting the room passes through HEPA filtration. All waste and water lines are protected and separate. The 15 patients are being individually monitored. 

How are the pilots, crew members, and other staff involved in transporting the passengers protected from exposure to the virus?

MA: No commercial airlines were used. The American citizens were wearing personal protective equipment, so wearing gowns, masks, eye protection. The staff that flew and traveled on and [handled boarding and deplaning], all had additional training and protective equipment. This is part of a well-coordinated effort that has routine drills, education and competencies.

If, during those 42 days, the person is determined to be negative and asymptomatic and can be monitored in their home state, they would not travel commercially. Instead, they would use private air or ground transportation. That will all be done in conjunction with ASPR (Administration for Strategic Preparedness and Response, an operating agency under the HHS that responds to public health emergencies). 

How worried are you about the Andes strain’s capability to transmit person to person? 

MA: Hantavirus itself is not new and has been known for decades. Of the known strains, only the Andes variant has been shown to spread from person to person, which is the strain involved in this case.

Transmission of Andes hantavirus has only been documented from symptomatic individuals, people who are actively ill, to others who have had prolonged, close contact, generally defined as at least 15 minutes within six feet. There are no documented cases of transmission from an asymptomatic person.

That said, we're not taking any chances. Everyone currently in quarantine will remain there until authorities are confident they are no longer transmissible. The incubation period for the Andes virus is believed to be up to 42 days. Those individuals will be monitored closely for at least 72 hours while officials conduct additional interviews, proximity [assessments] and epidemiology evaluations. 

How will patients in quarantine be monitored and tested for hantavirus, and how does it differ from COVID procedures?

MA: Two things will happen. At a minimum, individuals will be monitored throughout the day for any symptoms. If they develop symptoms at any point, they will undergo hantavirus testing, including PCR testing. Unlike a simple positive-or-negative home COVID-19 test, PCR testing can measure how much of the virus is present in the bloodstream. If individuals remain asymptomatic and are considered to have little to no exposure risk, they would not undergo routine testing.

We worked in conjunction with the CDC and the public health labs to be able to test for the specific [Andes] strain. Because the strain is rare in the United States, such testing is not widely available across the country. That's something that we've worked to be able to provide in our facility, in order to provide rapid turnaround times. 

Does the presence of the virus in someone’s blood mean they are certain to become symptomatic later on?

MA: That is part of the reason we placed them in the biocontainment unit for closer monitoring. As this trip was an expedition and it went on for quite some time, it is possible they were exposed, and their own immune system was able to fight off the hantavirus. That is why they will undergo routine testing.

It is possible they may never become symptomatic, and we certainly hope that is the case. But out of an abundance of caution, we placed them in the treatment area and will continue to monitor them very closely.

How is Nebraska Medicine making sure medical staff don't get infected? 

MA: Each room has what is called negative pressure, with its own air supply. Water and waste are also specially treated to help ensure that, if a patient becomes symptomatic and is moved to the biocontainment unit, nothing is released back into the general population. Even the water is autoclaved. Everything is disposed of in an incredibly safe way. 

Staff members use additional personal protective equipment that provides an independent air supply to ensure they are not at risk of exposure to the virus. So that unit is completely compartmentalized from other patients. It is a very, very specialized unit—that's why there's so few of them in the country.

Can you explain what autoclave means?

MA: If you go to your dentist, all of the surgical instruments are autoclaved. The same thing for any instrumentation within the hospital. It's very high heat that destroys everything, and it destroys the virus. Even waste products that come from the person are autoclaved. 

Are you confident about Nebraska Medicine's ability to handle the hantavirus outbreak? 

MA: The highest confidence. Going back to 2014, we have safely treated highly infectious patients, including Ebola patients. We received patients with some of the first COVID patients in our country coming off of the Diamond Princess cruise ship. We have worked with our federal partners with ASPR, with the White House, Health and Human Services.

We've prepared for this. We run drills, we train our staff very carefully. This is part of our identity. We are one of the best prepared centers on the planet for situations like this.