Two-thirds of passengers from the coronavirus-stricken Grand Princess cruise ship that were quarantined at a California military base declined to be tested for COVID-19.

A federal official and some passengers said if they were tested upon arriving at the base, there would have been more compliance.

But the passengers are nearing the end of their 14-day quarantine, and if they accepted the testing now, they would have to stay longer.

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Two-thirds of the passengers from the coronavirus-stricken Grand Princess cruise ship declined to be tested for COVID-19, according to a report in The San Francisco Chronicle.

Of the 858 passengers that were quarantined at the Travis Air Force Base in Fairfield, California, 568 turned down testing, a federal official familiar with quarantine operations on the base told the Chronicle.

The Grand Princess docked in Oakland on March 9 across the bay from San Francisco with 2,422 passengers on board, 942 of which are California residents. Twenty-one people on the ship had tested positive for the virus, two passengers and 19 crew members. Sick passengers were taken to local hospitals and the rest were mandated to quarantine at US military bases for 14 days, with some going to Travis Air Force Base, which is about 55 miles outside the Bay Area.

Some passengers said they weren't aware that they even had the option to refuse. About 20 passengers exhibited symptoms since arriving at the base and were quarantined away from the others.

Vice President Mike Pence had previously stated on March 6 that all Grand Princess cruise ship passengers quarantined on the base would be tested. But a White House official told the Chronicle that "no one can be forced to be tested" and all passengers were monitored and offered testing.

The refusal to test could result in the hundreds of passengers "re-seeding their communities" when they're released, UCSF professor of epidemiology George Rutherford told the Chronicle.

The passengers are expected to be released next Tuesday. If they submitted to tests now, they would have to stay at the base longer.

"These folks know they are in a 14-day quarantine, if they test positive they are further delayed until they test negative," the official told the Chronicle.

Some passengers even told the Chronicle that federal health officials were advising them not to take the test if they didn't have any symptoms during the two-week quarantine on the base.

The tests were delayed when passengers deboarded the cruise ship and arrived at the Fairfield base, which is why the federal official, as well as some passengers, said there wasn't much compliance.

"If they had been prepared and given us the option from day one we were here, there would've been a much higher acceptance," Grand Princess passenger Robert Archer told the Chronicle. He was quarantined on the base with his wife.

Archer said they were told that they would be quarantined for 14 days on the base and then released if they didn't exhibit any symptoms. He and his wife live in San Francisco and told the Chronicle they would like to shelter in place in their home just like the rest of the city.

The Grand Princess isn't the first Princess Cruises vessel to experience a coronavirus outbreak. About 150 passengers that were aboard the Diamond Princess cruise ship were brought from Japan to Travis Air Force base on February 16. They were quarantined at the base for 14 days and released on March 2.