The Centers for Disease Control and Prevention revised its guidelines on Ebola transmission on Sunday night, urging survivors to abstain from all forms of sex or use condoms every time “until more information becomes available,” rather than three months as previously recommended.

The World Health Organization and Liberia have issued similar recommendations in recent weeks. They were acting on evidence suggesting that a Liberian man who recovered from Ebola might have transmitted the virus to his female partner many months later.

Ebola genetic material was found in a semen sample the man provided 175 days after he developed symptoms, 74 days longer than ever before found in a survivor. Scientists in Liberia have compared the genetic sequence of the virus found in the woman, Ruth Tugbah, 44, to partial sequences obtained from the virus in her boyfriend’s semen and in blood samples taken months ago from his potential contacts with Ebola, and found that they matched at several key points.

Thus far, the information is consistent with sexual transmission, scientists said, but not conclusive, and the study is continuing. Researchers at the C.D.C. were also trying to establish whether the sample the man provided contained infectious virus, rather than only harmless genetic material or RNA.