Nelson Mandela is unable to speak - Ex-wife

South Africa's former president, Nelson Mandela, remains "quite ill" and is unable to speak thus using facial expressions to communicate as he receives intensive medical care at home, his former wife says.

Winnie Madikizela-Mandela said the 95-year-old former president was not on life support, but he was no longer talking "because of all the tubes that are in his mouth to clear (fluid from) the lungs" and prevent infection form returning.

"He can't actually articulate anything as a result," she told The Sunday Independent. "He communicates with the face, you see. But the doctors have told us they hope to recover his voice."

"He remains very sensitive to any germs, so he has to be kept literally sterile," she said. "The bedroom there [at his home] is like an ICU ward."

Mandela was discharged in a critical condition on September 1 to his home in Johannesburg's upmarket Houghton suburb after nearly three months in hospital for a lung infection.