Passengers from hantavirus ship arrive in US; 3 people in biocontainment

The cruise ship rocked by an unprecedented Andes hantavirus outbreak arrived in the Canary Islands off the coast of Tenerife Island over the weekend and is being evacuated. At least one new case has been identified amid the disembarkment.

As of Monday morning, officials for the World Health Organization reported that the last of the passengers of the MV Hondius cruise ship are expected to be evacuated today. Thirty crew will remain on board and see the ship back to Rotterdam in the Netherlands. Prior to the evacuation there were 147 people on board.

All of those evacuated from the ship are being transported off the island on specially arranged repatriation flights, not commercial flights. The evacuations and flights are being coordinated by Spanish authorities as well as the WHO and other national health officials.

Amid the evacuations, one new case has been definitively identified in a French citizen who tested positive on the journey home. That brings the outbreak tally to nine cases. Of those cases, three deaths had previously been reported, including a Dutch couple and a German woman.

US passengers

There may be a 10th case in a US passenger; US health officials reported that a person tested “mildly positive” after being evacuated from the ship. But for now, the WHO is reporting that as “inconclusive” testing and is awaiting confirmation before updating the case count.

The information about that possible US case came on Sunday from a statement on social media by the US Department of Health and Human Services. The statement incorrectly said that federal and state officials had transported 17 American citizens who were on board the ship back to the US on a non-commercial flight. The repatriated US passengers were flown to Omaha, Nebraska, where the federal government has its only National Quarantine Unit on the campus of Nebraska Medical Center and the University of Nebraska Medical Center. The Nebraska Medical Center also houses a National Biocontainment Unit.

In a press briefing in Omaha on Monday morning, federal and Nebraska officials corrected the HHS statement, saying that the US has repatriated 18—not 17—people, which includes 17 US citizens and one person who is a dual British/US citizen. The passengers range in age from late 20s to late 70s–early 80s.

On the flight to Omaha, two were flown in special biocontainment units “out of an abundance of caution.” That includes the one person who tested “mildly positive,” and a second person who had symptoms. For now, the definition of symptoms is “liberal,” including anything as minor as nasal congestion, officials said in the press briefing.

Three people in US biocontainment

Of the 18 people, 15 (including the dual citizen) are asymptomatic and in the quarantine unit.

The person with the “mildly positive” test is being housed in the Nebraska biocontainment unit. That person is said to be asymptomatic for now. In the press briefing, officials offered only vague answers as to what they meant by “mildly positive.” But, they are likely referring to the cycle threshold (Ct value) for the real-time PCR test used to detect snippets of hantavirus genetic material to confirm an infection. The test does repeated cycles to try to amplify specific snippets of genetic material that may be present. A test is generally considered negative if there’s no clear signal after 40 cycles. But it’s not a precise cutoff, and faint signals that appear after 35 or more cycles may be seen as ambiguous—possibly an early or late infection when little virus genetic material is present, or possibly just contamination.

The remaining two passengers are a couple traveling together, one of whom is the person previously identified as having symptoms. They have been moved to a biocontainment unit together at Emory University in Atlanta. The reason for the move is to ensure that the biocontainment unit in Nebraska—which has a small capacity to isolate hantavirus cases—can reserve space in the event that any of the 15 in quarantine develop an infection, officials explained in the press briefing.

The quarantine period for those exposed to hantavirus is 42 days from their exposure date. The 18 people will be monitored carefully for the life-threatening infection, with the 15 in quarantine undergoing detailed risk assessments. Depending on various factors, some in the quarantine unit may be able to return home before the 42-day period. These factors include, among many things, their assessed exposure and risk levels as well as their access to care at home. People who develop hantavirus infections require high-level care. Thus, if people do not live close to health facilities with intensive care units or advanced life-support technology, namely ECMO (extracorporeal membrane oxygenation), they would likely be advised to stay in Omaha.

Transmission risk

Andes hantavirus is a rare infection in humans, and the vast majority of cases are acquired via exposure to rodents or inhaling particles from their droppings, urine, or bodily fluids. However, the Andes virus is the only hantavirus known to, in even rarer cases, spread from human to human, which appears to have been the case on the Hondius. Rodents have not been reported on the ship.

Cruise ships—where a mix of people from various places live in confined settings with communal facilities—are known to enable wide and rapid spread of viruses. While this is the first time an Andes virus outbreak with likely human-to-human transmission has occurred on a ship, no other features of the outbreak appear out of line with what’s known about the virus’s spread or disease. The virus transmits human-to-human amid close, prolonged contact with a symptomatic case. The virus is generally not known to transmit easily or from asymptomatic people. For more information about the outbreak and Andes virus, check out our explainer.

In addition to the 18 people returned to the US this weekend, six other American passengers on the Hondius had disembarked the ship in April before the outbreak was identified. They are being monitored by state health officials.