The 78-year-old was meant to have undergone an operation on Tuesday to repair damage to his skull from previous procedures.
He has spent much of the last three months in what Jerusalem's Hadassah hospital called "critical but stable condition".
Hadassah described his current infection as "mild".
Sharon was hospitalised in January after a brain haemorrhage and has since been in what doctors called a "critical but stable condition".
Since the stroke, Sharon has undergone several operations, including brain surgery, to stop bleeding in his head and the removal of some of his intestine.
Doctors have speculated that in the coming weeks Sharon will be moved to a nursing home intended for long-term comatose patients requiring constant medical care.
Sharon was replaced by Ehud Olmert as interim prime minister.
His Kadima Party, established by Sharon shortly before he was hit by the stroke, won a majority of seats in last week's Israeli general election.
Olmert is expected to succeed Sharon in the official capacity of prime minister in the coming weeks.