Military doctors are treating Nelson Mandela, the former President, for a recurring lung infection. The 94-year-old anti-apartheid leader remains susceptible to the ailment because of his age and his 27 years in prison.
Government officials revealed for the first time today why Mr Mandela had been admitted to hospital on Saturday, though they said he was responding to treatment.
Mr Mandela fought off a similar infection in 2011 and once contracted tuberculosis while imprisoned. Medical experts say respiratory illnesses such as pneumonia striking a man his age are a serious matter that require care and monitoring.
"They call pneumonia 'the old man's friend' because it is the thing that ultimately carries many people off," said Dr Peter Openshaw, the director of the Centre for Respiratory Infection at Imperial College's National Heart and Lung Institute in London.
"What I guess they'll be doing is trying to find out exactly which type of infection it is and then to give it the most appropriate treatment. With modern antibiotics and investigation, there's no reason a chest infection by itself should be untreatable."
The announcement ended speculation about what was troubling the ailing Mr Mandela. His ongoing hospital treatment has caused growing concern in South Africa, a nation of 50 million people that largely reveres Mr Mandela for bringing the country together after centuries of racial division.