First reported in 1996, the disease has spread widely, causing severe damage to the branched corals.
On some reefs near Key West, Florida, mortality of elkhorn coral has reached 95 percent, and the disease has been recorded in the U.S. Virgin Islands, Caribbean areas of Mexico, the Bahamas and Florida, said James W. Porter of the University of Georgia.
Porter and his research team traced the white pox disease that causes the problem to Serrate marcescens bacteria, which are widely found in the intestines of humans and other animals.
The findings are reported in Monday's issue of Proceedings of the National Academy of Sciences.
"Elkhorn used to be the commonest coral in the Caribbean, but now it has been proposed for inclusion on the endangered species list," Porter said. "Elkhorn coral is the giant redwood of the coral forest."
Asked how the bacteria got to the coral, he responded: "We don't know. ... We are investigating the possibility that the origin of the bacteria is human waste, but we don't know."
That is a crucial question in the Florida Keys, where most waste is treated in septic fields rather than undergoing extensive treatment to kill the bacteria.
"The implications for people in the Florida Keys are high," Porter said. Discussions are under way into improving wastewater treatment, he said, but it costs a lot and state and federal help are not assured.
"Everyone down here is in love with the water," he said. "They want to do the right thing, but the cost to maintain the highest water quality standards could be prohibitive for the individual citizenry."
Cheva Heck of the National Oceanic and Atmospheric Administration's Keys National Marine Sanctuary agreed that while the bacteria have an association with humans, "the research itself doesn't tell us where it comes from."
Dale W. Griffin of the U.S. Geological Survey's Center for Regional and Coastal Studies in Florida said he found it interesting that bacteria with a fecal source have been identified as pathogens in the reef.
"One of the primary concerns in the Florida Keys is the waste disposal problem," said Griffin, who was not part of the research team. He noted the paper made no conclusion about the source of the bacteria killing the corals.
Coral colonies affected by white pox have irregularly shaped white spots which eventually grow and kill the coral by consuming the thin layer of living tissue that covers a coral's limestone skeleton.
The bacteria can grow by as much as one-half square inch to three square inches daily.
Treating the infected coral also poses problems, as the bacteria have become resistant to antibiotics, Porter said in a telephone interview.
Meanwhile, stress caused by the warming of the waters in the region is weakening the corals, making them more vulnerable to infection, he said.
White pox disease has struck only elkhorn coral so far, something Porter found surprising.
Other corals have their own problems, such as bleaching when the algae that populate and build the corals die off. That problem that has been increasing, and many blame on global warming.
Coral reefs are under assault worldwide, according to the United Nations, which blames global warming, fertilizer and sewage runoff and even fishermen's use of dynamite in some areas.