Pope Francis has a “polymicrobial infection” of his respiratory tract that will require his hospital treatment to be changed, the Vatican said Monday, with tests indicating a “complex clinical picture” for one of the oldest popes in the church’s history.

The Vatican indicated that the pope was fighting a multiple-pronged infection requiring “adequate hospitalization.”

Pope Francis was admitted on Friday with a respiratory infection. The announcement on Monday did not provide further detail, but raised fresh concerns about the pontiff’s health.