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.