MONROVIA, Liberia — Three members of a family in Liberia have contracted Ebola, two months after the country was declared free of the virus for the second time, health officials said on Friday.

The most recent outbreak, which officials are calling the fourth wave, was confirmed after a 15-year-old boy with symptoms of Ebola — including fever, weakness and bleeding — was admitted to John F. Kennedy Medical Center in Monrovia, the capital, on Tuesday, the Liberian health minister, Dr. Bernice Dahn, said at a news conference. The boy was then placed in isolation in the hospital.

Another senior health official, speaking on the condition of anonymity because he was not authorized to speak on the record, said the teenager was taken to the main Ebola treatment unit on Wednesday. He had started showing symptoms of Ebola last week, the official said.

The teenager’s test came back positive on Thursday, as did tests on Friday for his father and a brother, the official said, adding that at least seven health care workers may have treated the teenager without the protective equipment essential for Ebola cases. A key member of the contact-tracing effort said one nurse wore only regular gloves when treating the teenager, who was bleeding at the time.