Mandela, 94, was hospitalized with a recurrence of a lung infection that hospitalized him for the third time in four months and was likely pneumonia, ABC News said Thursday.
President Jacob Zuma's office issued a written statement saying the Nobel Peace Prize laureate was getting "the best possible expert medical treatment and comfort."
ABC said, according to medical experts, elderly patients were susceptible to pneumonia as their immune systems lose strength. Some don't show any sign of infection since their bodies aren't fighting it, but instead show signs of mental confusion.
Although the term "lung infection" often means pneumonia, it will take a lot of testing to confirm the diagnosis, doctors said.