Unlike diseases such as measles, which are highly contagious and spread easily, the Andes strain of hantavirus behind the outbreak is not that infectious.

Human-to-human spread is possible but the risk of infections globally remains low, says the WHO.

We are now closing our live coverage of this story, but you can keep up with all the latest developments here: US passengers from hantavirus-hit ship quarantined in Nebraska and Georgia

Matías Zibell
BBC Mundo

As Argentina's southernmost city, Ushuaia has long enjoyed its reputation as 'The End of the World' and as a gateway for trips both to Antarctica and for tourists to explore the dramatic, natural beauty of Patagonia.

But in recent days it has been grappling with a different kind of fame, one that has cast a shadow over local businesses and officials: the suggestion it could be ground zero for the hantavirus outbreak on the Dutch vessel MV Hondius.

One theory suggests a passenger may have been infected at a landfill site on the outskirts of Ushuaia, where tourists often visit to watch birds and where waste attracts rats and mice. Argentinian officials who spoke anonymously to some news outlets have said that is their leading hypothesis.

That suggestion, however, has not been well received locally.

You can read more about my trip to Ushuaia here.

Image source, WHO

We've also been listening to an update from the World Health Organization (WHO), which has been holding regular briefings on the hantavirus outbreak.

Dr Olivier le Polain, a public health physician and epidemiologist at the WHO, says it's possible further new cases will emerge in coming weeks.

But, he explains, that will likely be due to the long incubation period of the virus rather than ongoing community transmission.

On average, it takes three weeks for those infected to develop symptoms, he says, and in some cases it can be as long as 40 to 45 days.

"That’s why we need to remain vigilant, and make sure at the first signs and symptoms that people are being recognised, isolated and taken care of," he says.

Because of the long incubation period it will be another six weeks before passengers from the MV Hondius are given the all clear, which le Polain acknowledges will be a "difficult time".

Images from Omaha, Nebraska show agency staff helping with the disembarkation of passengers evacuated from the MV Hondius early on Monday.

Image source, Reuters

Image source, Reuters

Here is what we heard during today's press conference in Nebraska

• The risk to the public is "very, very low" health officials reiterated

• There are a total of 18 passengers who were taken to two US facilities
• 16 of the passengers were taken to a facility in Nebraska and two others were sent to Georgia
• The two individuals taken to Georgia include one individual who is symptomatic, but health officials cautioned that those symptoms could be indicative of another illness, not necessarily hantavirus
• One of the 16 individuals in Nebraska is a person who previously, before they arrived in the US, tested positive but is asymptomatic
• Of the people in Nebraska, 15 are in quarantine, and the one person who tested positive is in a biocontainment unit

There is a question about whether authorities can guarantee Americans won't catch hantavirus from the returning passengers.

The CDC's Dr Brendan Jackson responds that "there are no guarantees in life", but the safety of patients and locals is a top priority.

"We're putting as many measures in place as possible to ensure that people are safe and healthy, and we keep the community safe and healthy as well."

There's no plan in place for how frequently asymptomatic individuals will be tested at this time, says Michael Wadman, MD, medical director of the National Quarantine Unit, adding that frequency is being discussed.

He says officials are looking for symptoms similar to any influenza-like illness, such as fever, aches, dizziness, cough, shortness of breath, nausea, vomiting, diarrhoea etc.

Captain Michael Garner, a regional administrator for ASPR says two people being sent to Atlanta is part of a national approach so that patients are "load-balanced across the system".

The two people in Atlanta are a couple, only one of whom has symptoms.

The speakers are now asked about the numbers of passengers, which was originally said to be 17 but then rose to 18.

On this discrepancy, Matthew Ferreira from the Health and Human Services department clarifies the 18th person is a British dual national who decided to come back to the US.

That person remains in the quarantine unit in Nebraska, he says.

Dr Brendan Jackson of the CDC says close contact is usually considered to involve the exchange of bodily fluids like saliva, such as "sharing eating utensils, kissing, touching, those type of things".

"It can also mean just being really really close to that person for a fairly long period of time."

As a rough guide, he explains that means being within six feet for around 15 minutes, although he stresses there's "nothing magical" about those figures.

"It's not a force field, but it's a rough number that gives us a rough sense of how close somebody has been," he adds.

The CDC's Dr Brendan Jackson says state health departments have made contact with all passengers who have returned from the cruise ship.

"The state health departments have been monitoring them on a daily basis for symptoms and temperature checks," Jackson says of people who have travelled back to the US.

"They have plans in place to ensure they can isolate effectively in their homes should they develop symptoms," he adds.

The press conference has now finished, but we will continue to bring you the key lines from what we heard.

The fifteen passengers in quarantine in Nebraska will stay at the facility for assessment for the next several days, says Brendan Jackson. They are welcome to stay at the Nebraska medical facility longer, if they want to, he says.

Then there will be an individual monitoring plan to determine if patients could stay in isolation at home, or if they should stay at the medical facility for the full 42 days, Jackson says. This depends on each individual's living situation, how their health is and if they have access to high-level health care if necessary.

Jackson says they will "try to do this in the least restrictive way possible to protect the health of the passengers and their communities."

Dr Angela Hewlitt, medical director of Nebraska Biocontainment Unit, is now explaining the facility.

The quarantine unit, she says, is "much more like a hotel than a patient care space".

"We don't have the typical things that you'd see in a hospital room. It's a much more comfortable environment actually, with some things to help keep people comfortable, like exercise equipment."

By comparison, the biocontainment unit is used to house those who are ill, Hewlitt adds, saying there is currently one person in there.

"They are doing well, they currently do not have any symptoms, and have a good appetite, although they're very tired, understandably."

Michael Wadman, medical director of the National Quarantine Unit, says that the 15 passengers welcomed to quarantine this morning are in "good shape" and "good spirits" with a further patient in the biocontainment facility.

They were "definitely tired and needed some rest", he says.

Now they are focused on "symptom monitoring", but "everyone here is asymptomatic" and no one has a temperature, he says.

They're all resting now, he adds, and will undergo further assessment when they've had a chance to sleep.

Brendan Jackson confirms that sixteen passengers from the hantavirus-affected cruise ship were admitted to the University of Nebraska quarantine unit this morning.

Two other passengers from the ship are in Atlanta, he adds.

A reporter asks what it means for someone to have tested "mildly positive" for PCR if they don't have symptoms.

That patient's specimen was taken on the ship, not in the US, says Jackson.

He adds that there were two specimens collected from that patient, one of which was positive and the other negative.

"With these PCR tests... there's sort of a range in where they can fall. And so for that reason, we just want to make sure there's further testing to evaluate that."

The first question is about the person who is experiencing symptoms.

Brendan Jackson, MD, Centers of Disease Control and Prevention answers that to preserve space at the facility in Nebraska, some passengers were flown to Atlanta, including the passenger who displayed symptoms.

We should expect people to have symptoms, but that doesn't mean that they have this particular illness, he says.

Any symptoms of a mild cold would count as a symptom, he adds, and they are being extra cautious.

Dr Jeffrey Gold, president of the University of Nebraska, is coordinating the news conference and says it's an honour to help repatriate the American citizens.

"There is no place in the country that they could be better cared for," he says.

Gold adds that the university operates on a simple rule: "If we treat our patients the way we would treat our family members and loved ones, we're gonna be OK, and that's the rule."

He then begins taking questions.

Image source, AFP

We're also hearing from John Knox, who works on strategic preparedness and response at the US Department of Health and Human Services.

He says that 18 US citizens have been repatriated with the coordination of multiple federal agencies.

They were transported from the Canary Islands to Nebraska, and since touching down in the US have been taken to the University of Nebrasha Medical Center.

He says this facility was selected due to its "extensive expertise" as the only national quarantine unit in the country.

Knox says there are trained personnel "ready to safely handle situations like this", and that the operation so far "reflects strength of national preparedness system".

Over the next several days, the passengers will undergo health assessments, he adds.

Next to speak is Admiral Brian Christine, MD, Assistant Secretary for Health, at the U.S. Department of Health and Human Services, who says the risk to the public is still "very, very low".

Transmission takes close contact, he says, emphasising that "transparency has been and is the order of the day".

Nebraska Governor Jim Pillen says those quarantined at the facility will receive "the best world-class care possible".

He says the staff there are "highly trained and compassionate" and will make their stay "as comfortable as possible".

He reassures Nebraskans that there is a "strong plan in place" and local officials are working closely with federal agencies.

"No-one who poses a risk to public health is walking out the front door onto the streets of Omaha," he says.

Image source, AFP

The press conference from US health officials is expected to provide an update on the US citizens who have been exposed to hantavirus and are now back on US soil.

We'll bring you key lines as they happen. Watch live at the top of the page, and stick with us for the latest developments.