An adult in Colorado has died after a confirmed case of hantavirus that is not linked to a recent outbreak aboard a cruise ship in the Atlantic, Colorado Department of Public Health and Environment officials said in a statement on Monday.

The strain of hantavirus that caused the Colorado death occurs regularly in Colorado at this time of year, the statement said, and officials are investigating the source of exposure.

Hantavirus is primarily spread by rodents but can be transmitted between people ​in rare cases and after prolonged, close contact. Incubation can last about six weeks.

The Dutch-flagged MV Hondius cruise docked at Rotterdam on Monday. It had been ​carrying around 150 passengers and crew from ⁠23 countries when a cluster of severe respiratory illnesses was first reported to the World Health Organization on May 2.

Three people on the liner have died. Including those deaths, there have been eight confirmed and two probable cases on board, according to WHO.

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(Reporting by Daphne Psaledakis, Katharine Jackson; editing by Susan Heavey and Michelle Nichols )