The killer and mysterious coral disease that first struck Florida in 2014 has now reached the outer reefs of Key West and beyond, scientists say.

Now called stony coral tissue loss disease, the outbreak reached Looe Key in the Lower Keys last spring and seemed to contain itself.

But by December, it had landed at American Shoal and two weeks ago made it to the reef off Key West.

“We were really hoping the disease was going to fade before it got to these areas,” said Andrew Bruckner, research coordinator for the Florida Keys National Marine Sanctuary. “We’ve only seen it on four reefs, the areas in our sanctuary preservation, the outer areas that have the mooring buoys. None of this has shown up on the reefs close to shore. It’s only right now at this outer reef system.”

Bruckner said the disease has been spotted only on a few corals and has been spotted at Eastern Dry Rocks, about seven miles southeast of Key West.

The disease’s origin remains a mystery but researchers believe bacteria causes the disease and that it can be transmitted to other corals through direct contact and water circulation.

It carries high rates of mortality, the sanctuary says. Once a coral begins to lose living tissue, studies show the colony will die within weeks or months.

Typically when there has been a coral outbreak, it tended to stay in a certain area and then go into remission, Bruckner said. This one is far different.

“As we’ve been tracking this, we’ve seen the center of the outbreak continue to move,” he said. “Water currents transport it. It then gets to a new reef and is spreading.”

Scientists at Nova Southeastern University have been testing various treatments in their labs and have worked with other agencies to try to treat the disease in the water.

After applying antibiotics to coral in the lab, scientists came up with a way to do it in the water.

“It’s very time-consuming,” Bruckner said. “There’s no way we’d be able to treat every coral with the disease. We’re targeting the coral that have the most value — that provide the most habitat structure, the biggest, boldest coral.”

Divers are being asked to fully clean and decontaminate their gear after diving the reefs where the disease has been found. Instructions for decontamination are available here.

The disease first appeared off Virginia Key in 2014 and began spreading north, south and west, invading Florida’s reef system, the third-largest living reef on the planet and the only barrier reef system in the continental United States.

Last September, a researcher predicted the disease would hit Key West by the fall. The disease has touched more than half of Florida’s reef tract and shows no sign of stopping.

“This has lasted four-and-a-half years and the disease is still going strong,” Bruckner said.