Two more Women's and Children's Hospital doctors have been confirmed with whooping cough in Adelaide.

There have now been three cases in recent weeks.

Nine adults and 41 babies who were patients at the hospital have been offered antibiotics as a preventative measure.

The hospital says the doctors have contracted the infection despite keeping their vaccinations up to date.

One of the doctors diagnosed over the weekend also worked at North Eastern Community Hospital in Adelaide.

Another 46 patients there have been offered antibiotics.

There has also been a recent infant death in Adelaide from whooping cough.

Dr Brian Wheatley, from the hospital, concedes vaccination is not always effective.

"While the vaccine is extremely effective in preventing severe disease, it does not always prevent infection in all people," he said.