After the 94-year-old anti-apartheid legend spent a third night in hospital, doctors are saying they have drained excess fluid from his lungs to tackle the infection.
"This has resulted in him now being able to breathe without difficulty. He continues to respond to treatment and is comfortable," President Jacob Zuma's office said through a statement.
In the first detailed mention of his medical condition since his hospitalisation, the statement said he had "developed a pleural effusion which was tapped".
Previous medical reports since he was taken to hospital late on Wednesday have said he was responding well and that he was in "good spirits".
The successive bulletins have appeared to indicate that the recurrence of the lung infection afflicting the revered statesman and Nobel Peace Prize laureate is being successfully treated.
Global figures such as US President Barack Obama have sent get well messages and South Africans have included Mandela in their prayers on the Easter weekend, one of the most important dates of the Christian calendar.
Mandela became South Africa's first black president after winning the country's first all-race election in 1994.
A former lawyer, he is revered at home and abroad for leading the struggle against white minority rule – including spending 27 years on Robben Island and other prisons – and then promoting the cause of racial reconciliation. – Reuters.