By Luis Martinez / ABC News

At least 36 sailors aboard the Navy aircraft carrier USS Theodore Roosevelt have now tested positive for the novel coronavirus as of Friday, according to a U.S. official. Navy officials expect the number of sailors infected to continue to grow as the entire ship’s crew of 5,000 is tested for the virus during a port visit to Guam.

The carrier arrived in Guam on a previously scheduled port visit that turned out to be very timely because it afforded better facilities to th sailors who tested positive for COVID-19, and will make it easier to test the ship’s crew while it is pier side.

Earlier this week the Navy disclosed that three sailors aboard the carrier had tested positive, marking the first time that infections had been detected aboard a U.S. Navy ship at sea. By the time the ship arrived in Guam early Friday, the number of cases had grown to 25 according to a U.S. offiicial.

The growing number of positive tests are a major cause of concern to defense officials, as the tight quarters in aircraft carriers hold the potential for even more infections among the ship’s crew. That led to the decision to test the entire ship’s crew for the virus.

General John Hyten, the vice chairman of the Joint Chiefs of Staff told reporters Friday that it is expected that the testing of the ship’s crew could take as long as a week.

“As testing continues, additional positive cases of COVID-19 have been discovered aboard USS Theodore Roosevelt,” Admiral Mike Gilday, the chief of naval operations, said in a statement issued Thursday. “We are taking this threat very seriously and are working quickly to identify and isolate positive cases while preventing further spread of the virus aboard the ship.”

He added, “No Sailors have been hospitalized or are seriously ill.”

At an earlier Pentagon briefing on Thursday, Thomas Modly, the acting secretary of the Navy, told reporters that the increase in infected sailors would lead to testing of the ship’s entire crew.

Modly said the aircraft carrier would remain pierside in the U.S. territory with the crew limited only to the ship’s pier. A U.S. official told ABC News that the carrier is expected to arrive in Guam late Thursday.

“Our medical team aboard USS Theodore Roosevelt is performing testing for the crew consistent with [Centers for Disease Control and Prevention] guidelines, and we are working to increase the rate of testing as much as possible,’ Gilday said in his statement.

“Immediate priority will be symptomatic Sailors, those in close contact with Sailors who have tested positive already, and essential watch standers,” he continued. “We are isolating those who test positive. Testing will continue as necessary to ensure the health of the entire ship’s crew.”

Modly had earlier described the symptoms of infected sailors aboard the carrier as being “very mild” — namely body aches and sore throats.

Gilday said he expected additional positive tests to emerge after the large scale testing of the ship’s crew begins and that any sailors who test positive will be transported to U.S. Naval Hospital Guam for further examination. “We’re taking this day by day,” he said. “Our top two priorities are taking care of our people and maintaining mission readiness. Both of those go hand in glove.”

Gilday added, “We are confident that our aggressive response will keep USS Theodore Roosevelt able to respond to any crisis in the region.”

On Tuesday, Gilday told reporters it was unclear if the sailors became infected with the coronavirus following the ship’s most recent port of call in early March to Da Nang, Vietnam.

“It would be difficult to tie down these active cases to that particular port visit,” he said. “We’ve had aircraft flying to and from the ship and so we just don’t want to say that it was that particular port visit.”

Gilday said that prior to the port call in Vietnam, Navy officials carefully considered whether to proceed with the visit. He noted that at the time of the scheduled port of call there were only 16 cases of COVID-19 — all of them in northern Vietnam, far from the port located in central Vietnam.

Careful screening of returning sailors was carried out before they boarded the carrier, which then followed the Navy’s new guidance to maintain 14 days at sea following a port of call, officials said.

The first three sailors tested positive 15 days after the port of call.

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