The American doctor who was on the ship and initially tested positive has since tested negative and says "there's no evidence that I've had hantavirus."

A doctor from the biocontainment unit in Nebraska said the initial test was most likely a falsely positive, based on further testing.

Dr. Stephen Kornfeld -- the only American to test positive for hantavirus -- came down with flu-like symptoms on the cruise ship, and on Monday he was admitted to the University of Nebraska Medical Center's biocontainment unit following a positive test, officials said. The Bend, Oregon, resident has since tested negative and was cleared to relocate to Nebraska's quarantine unit, where 15 other passengers from the cruise ship who do not have symptoms are being monitored.

"I physically feel great -- I have felt great for many, many days," Kornfeld told ABC News. "Emotionally I feel wonderful. It's nice to be negative for hantavirus."

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A team of Argentine scientists are planning to head to Ushuaia next week to conduct research to see if hantavirus was already there before the MV Hondius cruise ship departed on April 1, officials said.

The team will collect samples and send them to a lab. The results are expected to come back in about four weeks.

The World Health Organization has posited that the first infection likely happened on land before the ship even sailed. But local officials in Ushuaia say they are not convinced because they’ve never had a confirmed hantavirus case there.

“Its been 45 days since the ship left and we haven't had any cases,” said Juan Petrina, director of epidemiology for Tierra del Fuego province.

-ABC News' Dragana Jovanovic

Officials at Radboudumc hospital in the Netherlands say blood tests show that the 12 hospital employees placed in precautionary quarantine were not contagious to others.

The hospital said the chance of actual infection remains "very small," but the employees are continuing a six-week precautionary quarantine.

-ABC News’ Will Gretsky

There are 41 people under monitoring across the U.S. for potential hantavirus infections, the Centers for Disease Control and Prevention's incident manager for hantavirus, Dr. David Fitter, said in a phone call with reporters.

Those 41 people include: 16 people who were repatriated from the cruise ship and are under quarantine at a Nebraska facility; two who were repatriated from the cruise ship and are being monitored at an Atlanta facility; seven people who were former cruise ship passengers who left before the outbreak was declared; and 16 people who were exposed during travel, including on flights, officials said.

No Americans are positive for hantavirus at this time, officials said.

All 16 people in the Nebraska facility are recommended to stay for the entire 42-day period, officials said.

The remaining exposed people who are not at the quarantine facilities are recommended to stay at home, away from others, with an emphasis to avoid travel, officials said. These individuals are in touch with their state and local health departments and the CDC said it is in touch with those departments.

-ABC News’ Youri Benadjaoud

On Monday, 16 American cruise ship passengers arrived at the University of Nebraska Medical Center; 15 are in the quarantine unit and one person who tested positive is in the biocontainment unit.

Three of those passengers now in Nebraska are residents of New York, according to New York state Health Commissioner Dr. James McDonald.

“One passenger is from New York City, while the other two are residents of Orange County and Westchester County. All three are expected to be subject to a 42-day monitoring period," McDonald said in a statement.

“It is important to emphasize that there is no immediate risk to the public,” McDonald added.