WASHINGTON (Reuters) - All 5,000 personnel aboard the U.S. aircraft carrier Theodore Roosevelt will be tested for the coronavirus in Guam after the number of confirmed cases on the ship rose to about two dozen, U.S. Navy officials said on Thursday.

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The infections aboard the carrier are one of the most vivid examples of the coronavirus’ impact on the military and could test the Navy’s ability to forge ahead with operations.

“We are in the process now of testing 100 percent of the crew of that ship to ensure that we are able to contain whatever spread might have occurred there,” Acting U.S. Navy Secretary Thomas Modly told a Pentagon news conference.

In all, eight sailors had tested positive for the coronavirus, up from three on Tuesday, Modly said.

Defense Department officials, speaking on condition of anonymity, said later, however, that the number of infected sailors had increased to about two dozen and would likely rise further as more were tested for the highly contagious respiratory illness.

Chief of Naval Operations Admiral Mike Gilday acknowledged in a statement that the number of confirmed cases continued to increase, but did not provide a number. He said the carrier had been in Guam on a port visit, during which time base access would be limited to the pier for the Theodore Roosevelt’s sailors.

“No base or regional personnel will access the pier,” Gilday said.

Gilday said naval medical facilities in Guam would allow him to “more effectively test, isolate, and if necessary treat sailors,” but stressed that none of the sailors were seriously ill.

“We expect additional positive tests, and those Sailors who test positive will be transported to the U.S. Naval Hospital Guam for further evaluation and treatment as necessary,” he said.

The nuclear-powered Theodore Roosevelt, a small city at sea, usually also includes naval aviators and Marines.

Earlier this month, the carrier visited the central Vietnamese city of Danang. Vietnam has only about 150 known cases of the illness that has infected more than 500,000 people worldwide.

As of Thursday, 280 U.S. service members around the world had tested positive for the coronavirus, including 104 from the Navy.

“We are trending higher,” Modly said, adding it was too early to say why that was the case.

While seeking to shield its own forces from the virus, the Navy is also moving to ease the strain on overwhelmed hospitals during the U.S. epidemic. It is sending a 1,000-bed hospital ship to New York City and another one to Los Angeles to treat non-coronavirus patients.

Pentagon officials have stressed that the U.S. ships are not set up for quarantining patients and say the close quarters makes it easy for viruses to spread.