The Food and Drug Administration has granted emergency approval for a new diagnostic kit to test blood for the deadly Ebola virus, even as doctors are reporting a survival rate in one hard-hit area that has climbed to about 70 percent.

The FDA announced the move Wednesday after posting the approval on its website a day earlier. It’s the latest in a series of emergency authorizations after the federal government declared that the ongoing health crisis warranted the use of testing methods that have not cleared the ordinary regulatory approval process.

It also came as officials with the Centers for Disease Control and Prevention said Wednesday that a technician working in a secure Atlanta laboratory may have come into contact with a small amount of a live virus that was part of an Ebola experiment.

CDC spokeswoman Barbara Reynolds said in an email that the worker was being monitored for possible exposure.

The blood-testing kits — part of an effort to be more proactive than responsive in the handling of the disease — earned the FDA’s seventh emergency authorization since October after Health and Human Services Secretary Sylvia M. Burwell in August declared that circumstances exist justifying the use for unapproved diagnostics to detect the Ebola virus.

The justification was based on a 2006 determination by then-Homeland Security Secretary Michael Chertoff that the Ebola virus presents a material threat against the United States population sufficient to affect national security.

The United States has seen four confirmed cases of the virus so far — three health care workers and one man, Thomas Eric Duncan, who died in Texas after contracting the virus in Liberia.

On Wednesday, Liberia’s U.N. peacekeeping mission reported its fourth Ebola case. A U.N. spokesman said in a statement that the infected worker was from Liberia and was transferred to an Ebola treatment unit.

The statement said the mission was taking “all necessary measures to mitigate any possible further transmission — both within the mission and beyond.”

Two U.N. staffers who contracted the disease have died.

The 2014 Ebola outbreak in West Africa was the largest outbreak of the disease in history, killing over 7,500 people in Guinea, Liberia and Sierra Leone, according to figures released Wednesday by the CDC.

But a year after the start of the outbreak, doctors are reporting signs of improvement, with survival rates in Sierra Leone dramatically increasing. According to a letter written by several doctors published online Wednesday by the New England Journal of Medicine, about 70 percent of Ebola patients are surviving the virus despite the absence of a vaccine.

In the letter, doctors describe 581 cases they dealt with at an Ebola treatment center in Sierra Leone’s capital, Freetown, in late September. About 31 percent of the patients died, including 38 people who were dead upon arrival. But even those numbers appear to be improving. Among patients admitted since Nov. 5, mortality rate was less than 24 percent.

The figures compare to a 74 percent death rate for 106 patients who were treated in the eastern Sierra Leone town of Kenema in May and June, when some health workers were on strike and response to the outbreak was in crisis mode.

The spread of the outbreak has slowed significantly, according to the CDC, which gave a worst-case scenario estimate of as many as 1.4 million cases by mid-January if the region did not receive more aid. Last month, the agency said that prediction would not happen.

“There’s been real momentum and real progress,” CDC Director Thomas Frieden said Monday after his second trip to Ebola-stricken countries. “The challenge is not to let up.”

• This article is based in part on wire service reports.

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