The Department of Human Services says DNA tests have linked the strain of the virus found in the women to the strain the doctor has.
The doctor has not been named, but he was working at an abortion clinic in Melbourne between June 2008 and December 2009.
Critics say the public should have been notified about the possibility of infection far sooner.
Hepatitis C takes a long time to surface. It can cause fatal liver problems and is very hard to treat.
People with the infection can pass it on if their blood gets under the skin or into the bloodstream of another person, possibly through the use of a shared syringe.
Dr Carnie says he cannot explain how 12 people could be infected by accident.
"Accidents might involve say one or two patients, but we are dealing with a cluster of 12 patients. So at this stage there is nothing in the processes and procedures at this clinic that would enable me to explain how it happened," he said. Continued
There number of cases of hepatitus C has now jumped to 22. Now, there are fears that the number of cases of hepatitus C are going to rise.
H/T ABC News