WASHINGTON (Reuters) – A U.S. sailor aboard a warship ship tested positive for the coronavirus for the first time, the U.S. Navy said on Sunday, as it disclosed the case of a person assigned to an amphibious assault ship at port in San Diego.

The Navy said the sailor was quarantined at home and that personnel who had been in close contact with the sailor have been notified and are in self-isolation at their homes.

“None of them is aboard the ship currently. U.S. Navy ships conduct routine, daily cleanliness procedures geared toward health, wellness and the prevention of communicable disease spread,” the Navy said in a statement.

The sailor had been assigned to the USS Boxer, the Navy said. A U.S. official, however, said the ship was in port, a substantially less risky situation than being under way at sea.

It was not immediately clear whether the sailor was sleeping on the ship or just working onboard during the day.

The case is the latest example of how the U.S. military is grappling with coronavirus cases around the world, from a Marine who works at key defense agency near the Pentagon to a soldier assigned to U.S. Army Europe Headquarters in Wiesbaden, Germany.

A dangerous virus on a warship presents particular concerns, as sailors operate in close proximity to one another.

The Navy said the USS Boxer was conducting a thorough cleaning, according to specific guidance from the U.S. Centers for Disease Control and Prevention and the Navy-Marine Corps Public Health Center.

It also said the military was conducting contact tracing to determine whether anyone else may have been in close contact with the sailor.

“Depending on the results of that investigation, additional mitigations may be taken,” the Navy said.