During a news briefing about the decision, Dr. Michael J. Ryan, deputy director of W.H.O.’s health emergency program, said that the recent increase in cases actually reflected a positive development: By earning the trust of some communities, medical teams have gained access to areas they had been unable to enter before, and are finding more patients.

Fear and distrust of the government run deep in the region, and extend to the Ministry of Health and organizations thought to be associated with it, including aid groups and the W.H.O. Suspicion has led some people to avoid testing and treatment altogether, or to postpone it until they are too sick to be saved.

A particular concern is that many deaths have occurred in the community, rather than in treatment centers. Keeping the sick at home helps spread the virus, because the disease becomes more contagious as it progresses. It is spread by bodily fluids, so caregivers who lack protective gear are almost certain to become infected, as are those who prepare corpses for burial.

Some of the anger and distrust stem from the way aid groups have operated, said Dr. Natalie Roberts, the emergency operations director for Doctors Without Borders. She said people in the communities did not understand why those with potential Ebola symptoms like fever, even children, would be isolated for up to 48 hours while waiting for test results, and why those who tested negative might be released without a diagnosis or treatment for their fever, which might well be malaria.

Dr. Roberts said the group was changing the way it deals with patients, letting them wait at home for test results, and making sure to address their other health concerns and provide needed information. Her organization is also trying to give patients choices, and allow them to be treated in local health centers rather than Ebola treatment centers if that is their preference.

Other groups are also changing their approaches to bring them more into line with what communities need, Dr. Ryan said, though he added, “We evolve the response, we don’t change it.”