Eight additional sailors who had returned to the USS Theodore Roosevelt aircraft carrier have retested positive for coronavirus, a defense official told CNN.

The sailors were initially removed from the ship to self-quarantine and were allowed back on board after testing negative twice.

The official said it is not clear if the sailors were reinfected or if very low levels of the virus remained in their bodies that testing had not detected.

The news comes after five other sailors retested positive earlier this week.

The new positive tests were first reported by Politico.

Some background: In March, more than 1,000 sailors from the carrier’s nearly 4,900-member crew tested positive following an outbreak aboard the ship. The Navy had been returning sailors to the Roosevelt following a period of quarantine and isolation in the hopes of getting the aircraft carrier to sea as soon as possible.

The Navy said Thursday that more than 2,900 sailors have been moved back on board.